Isn't it nice that Bob is playing with you? You're having fun, aren't you?
You're lucky that Bob is playing with you. You boys are having a good time.
例えばTohaさんのお子さんと遊んでくれている子がBobだとすると、下のように言えると思います。
Isn't it nice that Bob is playing with you? You're having fun, aren't you?
「ボブに遊んでもらっていいね。楽しいね。」
You're lucky that Bob is playing with you. You boys are having a good time.
「ボブに遊んでもらっていいね。（2人とも）楽しいね。」
ご参考になれば幸いです！
日本 
