A. There are a few ways to look at this. The cold truth is that while your kids may get along swimmingly, they're too young to get all broken up if they stop seeing each other. At that age, they're likely to move on pretty quickly.
But if the friendship is especially nice for your child and you're not interested in making the effort to patch things up with your ex-amiga, then grit your teeth and take one for your baby. Plan the kids' get-togethers at a neutral spot, like a playground or local pool, where grown-up conversations take a backseat to the kiddie activities you have to monitor.
If you're lucky, you'll meet another mom and make a new friend. And a new pal -- for your child and you -- might not be a bad thing anyway.