Not all kids sleep for 12 hours. IMO 7pm is particularly early to put kids to bed especially on holidays & especially a child of almost 4!
You are right: not all kids sleep for 12 hours. Not all kids are the same, some need more sleep than others. I am just saying that to me it does not sound like extremely early to put a kid of 4 years old to bed.
My kids are 6 years old and they go to bed at 7pm every night. Left to their own devices they will not wake up before 7.30 at the very earliest the next morning... And during holidays they are usually knackered and ready for bed by 6pm!
I just don't think you can deduce anything from the time they put their kids to bed. It certainly doesn't sound too early to me...
That does not mean I think they are guilty or innocent. I am very much still a fencesitter...