Some more points re children on folders.
We used a dahon curve (light bike with bigapples). We bought a. Telepcopic seatpost as over wise their was too much sticking out the bottom of the bike to go up curbs!
It fitted well and has the benefit of having a longer life as one size fits all. Therfoe the high cost is off set over the bikes life.
Sometimes children love a bike but don't actually like riding it functionally.
Ie if you take the "cool" onzo mini to a garden party it will be fought over all night by children. But they might not want to ride it all the time for outings.