As a non-SBR, the rifles may be able to be possessed by your children, without you being there, depending on the laws in that state. In case they wish to go target shooting or hunting squirrles on their own.
If they are SBR's, then it's more complicated for them to use them on their own, if that's the plan for you. You'll either need to be there at all times, or see if having them on the trust allows them to posses the NFA items by themselves. I would tend to doubt that, as it's at least 18 if not 21 to posses NFA items as an individual, so I would not think they could via a Trust.
Personally, for something non-tactical like a bolt action 22, I'd just leave it in 16" or longer configuration. It's not heavy like that anyway, and as others have said, there is a safety advantage early on with a longer rifle, as the danger is at the end of it all.