I wonder what kind of adult he is going to be after being so spoiled.
I can't imagine what kind of person he is going to be with his parents spoiling him so badly.
1) I wonder what kind of adult he is going to be after being so spoiled.
「あんなに甘やかされるとどんな大人になっちゃうんだろう。」
「甘やかされる」は being spoiled
2) I can't imagine what kind of person he is going to be with his parents spoiling him so badly.
「親があんなに甘やかして、どんな大人になっちゃうんだろう。」
「ひどく甘やかす」は spoil 人 so badly と言えます。
ご参考になれば幸いです！
I wonder how that kid is going to turn out with his parents spoiling him so much,
I wonder how that kid is going to turn out with parents like that.
子供が男の子なら、
❶I wonder how that kid is going to turn out with his parents spoiling him so much.
(あの子供はどんな大人になるんだろ？あんなに親に甘やかされて)。
子供が女の子なら、
❶I wonder how that kid is going to turn out with her parents spoiling her so much.
❷I wonder how that kid is going to turn out with parents like that.
(あの子供はどんな大人になるんだろ？あんな親をもって)。
turn out-最終的な結果。
The library turned out to be fun. (図書館は結果、楽しかったよ)。
He turned out to be really nice, (彼は結果、いい人だった)。
という風に使います。
参考までに！
I wonder how that kid will turn out after being spoiled so much
I wonder what happens to spoiled children when they become adults
I wonder how that kid will turn out after being spoiled so much
「あんなに甘やかされるとどんな大人になっちゃうんだろう。」
んだろう
・I wonder
とどんな大人になっちゃうんだろう・甘やかされる結果
・How that kid will turn out
あんなに甘やかされると
・after bring spoiled so much
二つ目はより一般的な思いだったら使います。
あんなに甘やかされる子供はどんな大人になっちゃうんだろう
I wonder what happens to spoiled children when they become adults
ご参考になれば幸いです！
日本 
アメリカ合衆国 
