Captain Mid,
I can go to PI every night because I don't have kids! But, small kids are allowed at PI with adults. They're not allowed in all the clubs (some of the dance clubs have age limits) but I see them in the ones I go to. They may get pretty grouchy staying out till 1:30 every night, though! And I'm not going to get into the ever-popular debate about whether kids have any business at PI at all. I think that's up to the parents.
Also, with no kids I don't have to make it for early entry to the MK, so I have lots of time to sleep off PI...