At the top of both the Peyresourde and the Tourmalet there are cafes that sell the usual, Restaurant at top of Tourmalet isn't bad food wise but on race day will be busy, if you can carry supermarche offerings then you would save £££, and avoid long queues.
Make sure you take plenty of sun cream and shade for the youngster, the tarmac was melting when we where at the summit of the P'ourde a coupe of years ago.
The French go mad for the 'crap' thrown out from the caravan so it can be a bit of a scrabble between the kids (depending on young ones age)