It's War! Ben Affleck & Jennifer Garner Battling Over Their Kids — Who'll Get Custody?

As Jennifer Garner and Ben Affleck's marriage crumbles, RadarOnline.com has learned that their children — Violet, 9, Seraphina, 6, and Sam, 3 — have become a point of serious contention.

After one disagreement involving the children's school, an insider told RadarOnline.com, "Jen went ballistic. Ben felt Jen overreacted, and that led to a huge divide between them.”

"Ben felt she wasn't supporting him and vice versa. His friends have tried to advise him that he has to support her, but Jen feels he left her hanging."

And with tensions rising, the source claims, it seems Affleck, 42, has thrown in the towel.

"He hasn't gone back to her to try to fix her hurt feelings,” the source said. "Like, he just doesn't care. Ben doesn't want drama so he hasn't confronted her.”

Instead, as RadarOnline.com has reported, he's snuck off to Las Vegas for late-night poker sessions, on both May 3 and May 14 — when Garner, 43, was in New York on business

Meanwhile, Garner has moved to Montreal for the summer to film her next movie, Nine Lives, and the children are likely to join her.

And according to an insider, it's an arrangement that could become permanent. In an event of a divorce, said the source, "Jen's going to try for full custody."