✨ Best Answer ✨
・I agree, because I feel I spend too much time online.
→ I agree because I feel I [also] spend too much time online.
※, because:カンマ(,)不要
・Many children use phones or computers to play games and watch YouTube every day.
→ Many children use [their smartphones] or computers to play games and watch YouTube every day.
・〇 They should study and talk with their family or friends more.
・But some of them use it as a study tool.
→ [However,] some of them use [their smartphones or computers] as a study tool.
※But:独立した文の文頭には使わない。They should study …, but I think ….は可能
・I think depend on their heart. ← 意味???
→ I think [they should spend less time online].
ネットを使う時間をもっと少なくするべきだと思います。
※little(形容詞:時間などが短い) -less(比較級:もっと短い)
[ ]を付け足すか変更しています。
参考にしてください。