Wait I'm a little confused .Did he marked him? Don't the usual biting is behind the neck?

It varies! Anywhere near the neck can be marked tbh. I actually was more surprised that the biting is behind the neck these days. I usually found where the biting happens near the collarbone/side of the neck in my early days of reading ABO

I see.thanks and I know It's too early to say this but I hope we get to see their kids in the future ヾ(❀╹◡╹)ﾉ~

I think it's whatever the author decides.

Seeing how on the raws the 5th chapter is named "Mark" we're to assume he was marked xD