I went through a brief phase of being a bit obsessed with that 'Girls Next Door' show and read all the tell-alls and Internet stuff. They definitely have kid-friendly events (the annual Easter party is supposed to be for kids/families; the Playmates and Girlfriends dress more modestly, there are activities designed for children, etc.). The Halloween party is the wildest and most X rated of the five big annual parties and not at all suitable for kids, although I guess a baby would be too young to know what's going on.
There's no way they'd invite a baby, though I am surprised he was allowed to bring the baby in. The security to get in is insane - you have to have an invite and ID which are checked at two different points, and apart from Hef's personal friends it's mostly celebs and hot women (but if you fall into the latter category and you show up having gained weight or not looking as hot as in your photos, you can still be turned away, even if you have an invite). An actress I was a fan of who's been on many men's magazine covers was invited once, but showed up with her uninvited husband who is a movie studio VP - he was not allowed in. So I guess they made allowances because he's a celeb, or perhaps he's friends with Hef. The party is outdoors so I hope they found a quiet room inside for him or perhaps one of the elderly female staffers offered to watch him.