It's natural that I should help. Don't worry about it.
It's natural to feel that way.
そう感じるのも無理ないね
It's natural for a baby to cry
赤ちゃんが泣くのは当然のことだ
It's natural that such a hard-working student should succeed
そんなまじめな学生が成功するのは当然だ
上記のような場合でnaturalという表現を使えますね。
It's natural that I should help.
（私が）手伝うのは当然のことだ
Don't worry about it
気にしないでね
ご参考になれば幸いです！
アメリカ合衆国 
