Ben's back on active duty with the kids! Affleck picked up daughter Seraphina and son Samuel from school on Friday -- which is a big deal because that means ex-wife Jennifer Garner has cleared him to be with the kids. It means she feels comfortable enough in Ben's sobriety that he can parent effectively and that he's fine being alone with the kids.

Jen has put a lot of demands on Ben following his recent stint in rehab -- requiring him to stay in out-patient treatment and even forcing him to dump his much-younger Playboy model girlfriend Shauna Sexton, 22, in order to help keep him on the straight and narrow.

Meanwhile, Jen's looking happy and healthy as reports claim the actress is dating someone new. She's not sitting around waiting for Ben to clean up his act -- she's DONE with him. We caught up with Garner after a parent session at the kids' school on Friday as she had an animated conversation with a friend ...