YOU SAID:

I went to the store to look for my son. I left him there on accident.

INTO JAPANESE

私は息子を探しに店に行った。私は偶然彼をそこに置き忘れた。

BACK INTO ENGLISH

I went to the store to look for my son. I accidentally left him there.

INTO JAPANESE

私は息子を探しに店に行った。誤って彼を置き去りにしてしまった。

BACK INTO ENGLISH

I went to the store to look for my son. I left him by mistake.

INTO JAPANESE

私は息子を探しに店に行った。私は間違って彼を置き去りにした。

BACK INTO ENGLISH

I went to the store to look for my son. I left him by mistake.