No, I've never lost any friends due to them having children. Maybe it's different for men though.
I am a Godfather to one of my best friend's sons. Having said that I could see why people might gravitate towards spending more time with those who are in the same boat as them.
Couples usually hang out with other couples and those with children probably attend each other's playdates, birthday parties, or take turns hosting sleep overs and baby sitting.
It's also not uncommon for their friends without children to pull away from them because they're tired of hearing about every single thing the children do.
It's good to maintain friendships with people who are where you are regardless of your status. Have some single friends, childless friends, married friends, or couple friends. This way you'll have friends to socialize with. :)