entity.go
func (e *BasicEntity) AppendChild(child *BasicEntity) {
	child.parent = e
	e.children = append(e.children, *child)
}
func (e *BasicEntity) AppendChild(child *BasicEntity) {
	child.parent = e
	e.children = append(e.children, *child)
}
// AppendChild appends a child to the BasicEntity