Better check out the boyfriend and the living arrangements very seriously.
I am thinking that too. Stealing the car and making a run for it with baby sister may have made perfect sense in the mind of the 9 year old autistic child. The overwhelming majority of times when I read or hear about the molestation of children the perp is usually mom's shack-up boyfriend.
If there’s not anything wrong, and it needs to be investigated, someone needs to keep a better eye on the car keys.