My 6 year old does find it claustrophobic so I normally get a middle pair with him or put him on the asile. Do try and get the last row in the front cabin on a 3 class 777 either centre or window as you can walk around to get out, the climbing over can be a pain. On a 4 class 777 I like row 10, missing window though.
Have a wonderful trip and make sure you ask the cabin crew for help with the seat/ divider if your not sure how to use them.
Joejet