Here's a chart to compare some of the slates and slabs that might help get the kids smudgy little fingers off you iPad - and occupy them for many car journeys in the future.
For older children and teenagers, the devices aren't that different from the adult ones except for the bright colours. Teenagers might actually prefer a more classic design. There are a couple directed at the 12 - 15 age group on the right here, but it might make as much sense to look at the general options available amongst the budget tablets or iPad Mini lookalikes.
Some of the ones here do have a little extra rubber to cushion them from the inevitable knocks and bumps. They do not, however, have any alternative to the rather vulnerable glass-fronted touchscreen. The only answer there really is to get one that's a little smaller - say 7-inch - to reduce the risk.