3-day bike tour with young kids. Scotland suggestions please

Am contemplating a wee tour with wife and 2 kids in August. I think we'll probably do it fully car-supported (I'll ride back to the start each day to get the car) and we're ambivalent about camping. Kids are 8 and 5. Here are some parameters:
 - Probably no more than 25km a day, ideally less
 - 3 days, maybe four
 - Fairly flat to accomodate the 5yo on a singelspeed
 - Scotland only please (we live up North so England is a billion hours of driving away)
 - As little car traffic as possible

Currently looking at the southern part of the Great Glen Way (prob go FW-FA) but open to suggestions elsewhere too. First impression of GGW is that accomodation might be limited but that was just a cursory google.

Any other suggestions to investigate?