They're doing it for the kids ... and that's not a bad thing.

While J.Lo and Marc Anthony might be separated, they came together so the family could spend Marc's 43rd birthday together in Miami.

Both hung by the pool in Miami over the weekend with 3-year-old twins Emme and Max at the Miami mansion they once shared. They announced the end of their seven-year marriage in July.

At a Miami concert on Friday, Anthony got emotional after fans sang "Happy Birthday" to him -- the singer, overwhelmed by the support, fell to his knees and cried.

Keep your head up, Marc!