diff --git a/Sources/FirebladeECS/Family.swift b/Sources/FirebladeECS/Family.swift
index eded766..2200402 100644
--- a/Sources/FirebladeECS/Family.swift
+++ b/Sources/FirebladeECS/Family.swift
@@ -161,7 +161,7 @@ extension Family {
         }
 
         mutating func aggregateRelativesBreathFirst(_ parent: EntityIdentifier) {
-            guard let children = nexus.parentChildrenMap[parent] else {
+            guard let children = nexus.childrenByParentEntity[parent] else {
                 return
             }
             children
diff --git a/Sources/FirebladeECS/FamilyTraitSet.swift b/Sources/FirebladeECS/FamilyTraitSet.swift
index bf1220c..685a76c 100644
--- a/Sources/FirebladeECS/FamilyTraitSet.swift
+++ b/Sources/FirebladeECS/FamilyTraitSet.swift
@@ -61,11 +61,13 @@ extension FamilyTraitSet: Hashable {
     }
 }
 
-extension FamilyTraitSet: CustomStringConvertible, CustomDebugStringConvertible {
+extension FamilyTraitSet: CustomStringConvertible {
     @inlinable public var description: String {
         return "<FamilyTraitSet [requiresAll:\(requiresAll.description) excludesAll:\(excludesAll.description)]>"
     }
+}
 
+extension FamilyTraitSet: CustomDebugStringConvertible {
     @inlinable public var debugDescription: String {
         return "<FamilyTraitSet [requiresAll:\(requiresAll.debugDescription) excludesAll: \(excludesAll.debugDescription)]>"
     }
diff --git a/Sources/FirebladeECS/Nexus+Component.swift b/Sources/FirebladeECS/Nexus+Component.swift
index 4a0ec73..9f1f053 100644
--- a/Sources/FirebladeECS/Nexus+Component.swift
+++ b/Sources/FirebladeECS/Nexus+Component.swift
@@ -34,7 +34,7 @@ extension Nexus {
 
         // add component instances to uniform component stores
         if componentsByType[componentId] == nil {
-            componentsByType[componentId] = ManagedContiguousArray<Component>()
+            componentsByType[componentId] = UnorderedSparseSet<Component>()
         }
         componentsByType[componentId]?.insert(component, at: entityId.id)
 
diff --git a/Sources/FirebladeECS/Nexus+FamilyUpdate.swift b/Sources/FirebladeECS/Nexus+FamilyUpdate.swift
index 2c1ab51..9b92e72 100644
--- a/Sources/FirebladeECS/Nexus+FamilyUpdate.swift
+++ b/Sources/FirebladeECS/Nexus+FamilyUpdate.swift
@@ -64,11 +64,11 @@ extension Nexus {
 
     final func add(entityWithId entityId: EntityIdentifier, toFamilyWithTraits traits: FamilyTraitSet) {
         precondition(familyMembersByTraits[traits] != nil)
-        familyMembersByTraits[traits].unsafelyUnwrapped.insert(entityId, at: entityId.id)
+        familyMembersByTraits[traits]!.insert(entityId, at: entityId.id)
     }
 
     final func remove(entityWithId entityId: EntityIdentifier, fromFamilyWithTraits traits: FamilyTraitSet) {
         precondition(familyMembersByTraits[traits] != nil)
-        familyMembersByTraits[traits].unsafelyUnwrapped.remove(at: entityId.id)
+        familyMembersByTraits[traits]!.remove(at: entityId.id)
     }
 }
diff --git a/Sources/FirebladeECS/Nexus+SceneGraph.swift b/Sources/FirebladeECS/Nexus+SceneGraph.swift
index d8576a4..24e8497 100644
--- a/Sources/FirebladeECS/Nexus+SceneGraph.swift
+++ b/Sources/FirebladeECS/Nexus+SceneGraph.swift
@@ -8,11 +8,11 @@
 extension Nexus {
     public final func addChild(_ child: Entity, to parent: Entity) -> Bool {
         let inserted: Bool
-        if parentChildrenMap[parent.identifier] == nil {
-            parentChildrenMap[parent.identifier] = [child.identifier]
+        if childrenByParentEntity[parent.identifier] == nil {
+            childrenByParentEntity[parent.identifier] = [child.identifier]
             inserted = true
         } else {
-            let (isNewMember, _) = parentChildrenMap[parent.identifier]!.insert(child.identifier)
+            let (isNewMember, _) = childrenByParentEntity[parent.identifier]!.insert(child.identifier)
             inserted = isNewMember
         }
         if inserted {
@@ -27,7 +27,7 @@ extension Nexus {
 
     @discardableResult
     public final func removeChild(_ child: EntityIdentifier, from parent: EntityIdentifier) -> Bool {
-        let removed: Bool = parentChildrenMap[parent]?.remove(child) != nil
+        let removed: Bool = childrenByParentEntity[parent]?.remove(child) != nil
         if removed {
             delegate?.nexusEvent(ChildRemoved(parent: parent, child: child))
         }
@@ -35,11 +35,11 @@ extension Nexus {
     }
 
     public final func removeAllChildren(from parent: Entity) {
-        parentChildrenMap[parent.identifier]?.forEach { removeChild($0, from: parent.identifier) }
-        return parentChildrenMap[parent.identifier] = nil
+        childrenByParentEntity[parent.identifier]?.forEach { removeChild($0, from: parent.identifier) }
+        return childrenByParentEntity[parent.identifier] = nil
     }
 
     public final func numChildren(for entity: Entity) -> Int {
-        return parentChildrenMap[entity.identifier]?.count ?? 0
+        return childrenByParentEntity[entity.identifier]?.count ?? 0
     }
 }
diff --git a/Sources/FirebladeECS/Nexus.swift b/Sources/FirebladeECS/Nexus.swift
index ffe17d2..5fdf2fb 100644
--- a/Sources/FirebladeECS/Nexus.swift
+++ b/Sources/FirebladeECS/Nexus.swift
@@ -6,40 +6,44 @@
 //
 
 public final class Nexus {
-    public final weak var delegate: NexusEventDelegate?
-
     /// Main entity storage.
     /// Entities are tightly packed by EntityIdentifier.
     @usableFromInline final var entityStorage: UnorderedSparseSet<Entity>
 
+    /// Entity ids that are currently not used.
+    @usableFromInline final var freeEntities: [EntityIdentifier]
+
     /// - Key: ComponentIdentifier aka component type.
     /// - Value: Array of component instances of same type (uniform).
     ///          New component instances are appended.
-    @usableFromInline final var componentsByType: [ComponentIdentifier: ManagedContiguousArray<Component>]
+    @usableFromInline final var componentsByType: [ComponentIdentifier: UnorderedSparseSet<Component>]
 
     /// - Key: EntityIdentifier aka entity index
     /// - Value: Set of unique component types (ComponentIdentifier).
     ///          Each element is a component identifier associated with this entity.
     @usableFromInline final var componentIdsByEntity: [EntityIdentifier: Set<ComponentIdentifier>]
 
-    /// Entity ids that are currently not used.
-    @usableFromInline final var freeEntities: ContiguousArray<EntityIdentifier>
+    /// - Key: A parent entity id.
+    /// - Value: Adjacency Set of all associated children.
+    @usableFromInline final var childrenByParentEntity: [EntityIdentifier: Set<EntityIdentifier>]
 
     /// - Key: FamilyTraitSet aka component types that make up one distinct family.
     /// - Value: Tightly packed EntityIdentifiers that represent the association of an entity to the family.
     @usableFromInline final var familyMembersByTraits: [FamilyTraitSet: UnorderedSparseSet<EntityIdentifier>]
 
-    /// - Key: A parent entity id.
-    /// - Value: Adjacency Set of all associated children.
-    @usableFromInline final var parentChildrenMap: [EntityIdentifier: Set<EntityIdentifier>]
+    public final weak var delegate: NexusEventDelegate?
 
     public init() {
         entityStorage = UnorderedSparseSet<Entity>()
         componentsByType = [:]
         componentIdsByEntity = [:]
-        freeEntities = ContiguousArray<EntityIdentifier>()
+        freeEntities = []
         familyMembersByTraits = [:]
-        parentChildrenMap = [:]
+        childrenByParentEntity = [:]
+    }
+
+    deinit {
+        clear()
     }
 
     public final func clear() {
@@ -60,11 +64,7 @@ public final class Nexus {
         componentsByType.removeAll()
         componentIdsByEntity.removeAll()
         familyMembersByTraits.removeAll()
-        parentChildrenMap.removeAll()
-    }
-
-    deinit {
-        clear()
+        childrenByParentEntity.removeAll()
     }
 }
 
@@ -77,7 +77,7 @@ extension Nexus: Equatable {
             lhs.freeEntities == rhs.freeEntities &&
             lhs.familyMembersByTraits == rhs.familyMembersByTraits &&
             lhs.componentsByType.keys == rhs.componentsByType.keys &&
-            lhs.parentChildrenMap == rhs.parentChildrenMap
+            lhs.childrenByParentEntity == rhs.childrenByParentEntity
         // NOTE: components are not equatable (yet)
     }
 }