Although there was a possibility that Raijin might take his belly button, he walked with his T-shirt pulled up, exposing his belly button.
こんにちは！
ご質問ありがとうございます。
ご質問について、いくつか言い方が考えられますが、例えば、
During the rumbling thunder, one of my children was walking with their shirt pulled up, exposing their belly button. Meanwhile, the other child was being cautious, making sure to cover their belly button so Raijin wouldn't take it, as they walked back home.
とすると、『雷がゴロゴロ音をたてている中、子供一人は肌着を着ていたけどTシャツをまくり上げながら歩き、もう一人は雷におへそを取られないように隠しながら歩いて家に帰りました。』となります。自分の子供という解釈で文章を作成しておりますが、そうではなくそういう子供を見たのであれば、one child として下さいね！
参考になれば幸いです。
He walked around with his T-shirt rolled up, even though the thunder might steal his belly button!
He walked around with his T-shirt rolled up, even though the thunder might steal his belly button!
・Steal his belly button
「おへそを盗む（取る）」という直訳で大丈夫です。Belly button（おへそ）。
・Rolled up / Tucked up
Tシャツを「まくり上げる」状態を指します。お腹を丸出しにして歩いているわんぱくな様子が表現できます。
日本 
アメリカ合衆国 
