Below a certain age you can dress children in whatever you like - and they don't care. But there comes a point where some things, such as Lycra skin shorts, become unpopular.
For anything other than racing, baggies are a good alternative. They're still comfortable because they're padded and they're seen as cool because they're for mountain biking. As your child probably owns a mountain bike anyway, it's a good match.
These Scott shorts are basically just scaled down adult baggies, with a synthetic padded Lycra inner short and a looser, stretch-nylon outer short. Inner and outer are stitched together at the waist but are otherwise separate, so there's no 'nappy effect' and there's no Velcro tabs or press studs to make the waistband uncomfortable. There's one Velcro-ed cargo pocket, which is big enough for mitts and/or an energy bar. The waist is elasticated, but I'd have liked to have seen a drawstring here too as the thinner of my two testers sometimes found them riding down slightly. They're not cheap shorts but comfort is good and my two testers (large 10-year-old and average 12-year-old) both liked them. The only shorts I've seen to rival these are Cannondale's Kids' Baggy Shorts and Polaris's Mini Freerides - both a tenner cheaper.