I absolutely love Alton Towers! Been going decades, since it only had one proper ride (the lovely Corkscrew) and went again this year and i still love it.
Remember the ride close time (which may vary from advertised time due to weather/busy-ness of park) is really the QUEUE close time - so it's worth going to your favourite ride, or the busiest, at the end of the day - and getting into the queue at 5 minutes to close of ride time.
Coach-trips tend to leave before the end of the day so it might get quieter for the last hour or so...
Th1rteen is our favourite ride - pleasant motion in an attractive woodland, and just thrilling enough for me - with a fun 'punchline' to it
- not too fierce, with no inversions, which I won't do these days because they make me feel a bit dizzy. An 8 and 10 year old would be a good age for it.
Wicker Man is fun but I found it a bit uncomfortable.
Use the Skyride cleverly, alongside the map, to plan to cut out some of the inevitable walking which will waste ride time, though if you all enjoy gardens there are very beautiful, and these days usually under-appreciated, areas of the park (let's face it though, mostly kids and adults are just keen to get on the rides.)
Try NOT to give in to requests to do the 'skill games' - people do win and you will see them walking round the park with huge stuffed animals etc - but it's really hard to make the ball stay in the bin or whatever. If you do have a go, try to hit the rim of the bucket/barrel so the ball runs around it and drops in, or try to put a bit of backspin on it (it's never worked for me but that's the advice I've read.)
Hopefully you'll have a wonderful day!