we went a couple of weeks ago - ds's aged 5 and 3. Agree that a taking your own food/drinks/snacks is a good idea. We always take a pushchair and load that with the food, spare clothes, towel, raincoats etc.
If it is at all warm the kids will want to go in the wet play area so you will need swimming trunks or spare pants and a towel - they do have stand in dryers, but a towel is useful.
SO much stuff to chose from, but mine like the driving school/L drivers, the helicopters, the maze, the large climbing playground in the wild woods, the spinning spider and the show on the lake at 12.00. We do the build and test workshop on the way out. 3d cinema is good too.
Tried the Fire Acadamy out for the first time - that was fun too.
ds1 won't go on the bigger rides, so there's loads of stuff we haven't done that looks good fun too. Still we've got season tickets, so hopefully will be expanding our repetoire later this yr.
BTW we got our season tickets by buying Lego in Jan (spend £70 for 2 x free tickets)- 2nd yr running - top tip for next yr.