We shall have to get him and the eldest cub together at some point, to see who would win in the 'whining world championships'
If you met us in Stamford Bridge (should be there around 11, hopefully a squeak before if we manage to set off on time!) and do the circuit from there it gives you a roughly 50km loop which includes Pooh Sticks bridge, the lunch stop and afternoon tea in Pocklington so it's in fairly manageable chunks - first third flat as a pancake, middle bit with lumps in, and the trip back to Stamford Bridge flat as a pancake again. The lumpy bit has one bit of a climb up to Givendale- but if it's too hard for either of them I'm sure I could arrange to accompany them on the 24" gear, a steady climb up through Millington and a couple of short stabby bits after Warter, with a couple of cracking descents to compensate.
I have always found that with the EldestCub he rises well to the challenge of riding with proper cyclists, and the whinge quotient diminishes hugely if it's not just me. But I don't know if that applies to yours! Alternatively, if you just wanted a nice easy sociable pootle with them you could always join us on the planets path on Sunday. Flat and traffic free run out to Naburn for a pub lunch, then (depending on time, weather and whether we can be arsed) possibly out to the outer planets and back, or possibly just back home.