Thankyou gift for boys aged 9 & 11

[Zil131]

My friends sons (9 & 11) are donating thier climbing frame to my sons (2.5 and 1). I thoght my boys should give them a thankyou gift; but as I am not yet familiar with this age group, I need suggestions please!
Thanks.

how much are you going to spend? If just a little thing from your kids then maybe a tennis or cricket set for the garden or if you are spending more one of those big garden games you can get like jenga or connect four in giant size (from M&S I think)