In reply to BusyLizzie:
I went with my 7 yo daughters (twins) up Pyg and Down Miners on Thursday. We stayed at YHA pen y pass night before to make it a bit of an adventure, and on the way up found a few little 'side scrambles' for fun. Llanberis is defo easier, but I find (previously) more tedious unless by bike. They found climb fine/ fun and descent hard work initially, but easy once down to miners track. Took us 6 hrs up and down with picnic by lake shore on way back down.
We played various games on the way up, such as 'things to do with mountains starting with a through z' (no x-ray fish here!), count the trainers, spot the people on Lliwedd/ crib goch, how valuable it quartz and how may crystals can you conceal in your pockets before i reveal it is not! etc etc...
Have fun, if the weather poo don't bother. If its mediocre do, and tell them how wonderfully well they have done (will be deserved anyway), if its great remember the sun cream!