Even if you don't get paid, look at the grandparent/aunt/uncles' position: have some fun with the baby, change some yucky diapers (ok not so fun), but in a short time you will be handing responsibility back to the parents, who will have to wake up in the middle of the night, night after night...
As both a repeat startup founder and a repeat parent of infants, I'll attest: the diaper-changing aspects are similar. You're doing it for love, not money or enjoyment. =)
Not too far off the mark. Once you get your head on straight, you can exploit any salaried job of at least some intrinsic worth as your own tool for business experimentation and even peripheral market research/experience.
So you're obviously not a parent, since you're not understanding that every parent sees your comment, agrees and thinks: Yeah, but I'd rather be a parent. :-)