This has never been the case before, and started showing up after the last patch.
When loading a game, where a child Sim was previously elsewhere (at a park etc) without a parent, the lot loads but NO active Sims are present, and the child's only option is "Care for self", they can not be returned to the lot. You have to click the arrow to either bring an adult to the lot you're on, or load into the lot the adult is on to regain access to the children (as if they were toddlers/infants). If you load to the parent, the children are still recognized as at the other location, and must be brought to the parent to be regained.
From the manage worlds screen, selecting a child in any household looks like this:
When clicking play on the family, the dialogue box to select which family member is show, but all children Sims have the same "cannot be played" message, and you MUST select an adult. Children are again still in their previous location, and must be brought to the adult to go back to wherever else they were and continue playing (away from the adult) as usual.
For family gameplay, this is highly disruptive.
