Put a blanket in the stroller so that it is more comfortable. The strollers at MGM are not as hard. I have a fear of this woman who sees them ONCE a year losing the twins. The boy twin has no fear and will go toward anything he likes. We have taken them twice already.
Cast members are very good at spotting lost children.
Disney also has surveillance cameras everywhere and a computer program that immediately broadcasts the description of the child and the status of the search. No paging is allowed, but in serious emergencies, Disney will notify cast members park wide. Disney only offers certain FastPass attractions where you can insert your pass and receive a time to return and enter without waiting. Everyone is entitled to FastPass who has park admission. Older teens should do well on their own.