All's fair in love and war and Ben Affleck and Jennifer Garner are big enough people (particularly Jen) to let bygones be bygones and reunite for the sake of their kids.

The successful co-parenters met up at the Violet and Seraphina's elementary school to escort the kids and meet the teachers. Little Samuel still has another year before he starts kindergarden so it was just the girls today.

After spending time in New York with girlfriend Lindsay Shookus, Ben flew back for the big day. Jen had taken the kids to Santa Barbara for a mini-vacay this past Labor Day weekend.

Jen sipped coffee and Ben had a smile on his face as they chatted and said hello to friends. Our photographer on the scene tells us, "They looked totally comfortable together and happy. It's like nothing every happened. Maybe they're better friends than spouses."

Could be true!