Its manwha about a man who isekai'd into a book he read, where the MC bullies the ML (his younger step brother). When he met the ML, he didnt want to bully him but the system punishes the MC if he doesnt
i think it's this ヾ(❀╹◡╹)ノ~
https://www.mangago.zone/read-manga/i_have_to_be_a_great_villain/
The childeen are so cute, especially Theo's twinヾ(❀╹◡╹)ノ~