Bladders
Twats everywhere
Yes please, might as well take a look. It's tricky to know what's best for them, my 4 year old is on my iPad 2 all the time, watching youtube (he's going to be swearing soon) and playing games. It'll be great if they can watch a film on the long trip to their grandparents too, and I think 7" screens will be fine.
There won't ever be a time (age) when they don't want one, so they'll use them until the break/become obsolete, so either buy cheap and replace in a couple of years, or buy a bit better and hope it lasts a little longer, I'm not sure which is the best route.
Have sent you a PM.