When people say that having a child takes over your whole life, they really mean it. For their first few months, they need you around them pretty much 24/7. When they're a little older, your day has to be planned around their school day, and their social events. It doesn't leave you with a lot of time to catch up with your own friends and family.
When you and your friends have children of similar ages, the problem becomes even worse. You might be free one day, but your friends aren't, and vice versa. Arranging to meet someone for a night out becomes almost a military operation, requiring delicate planning and weeks of notice. Remember when you could get a text message inviting you out, and you could accept it and be out half an hour later? No, us neither.