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. :-)
Actually, I am a parent and both of us, while we love our children and love to see them grow, are still tickled to be done with diapers. And when I hear a kid whine or a baby cry (out in public), it is music to my ears; That is not my kid crying, I don't have to do anything about it. A bit selfish yes, but an honest and natural feeling.
I've always approached those stressed out midnight feedings and diaper changes with enthusiasm though. Every time I take a look at my crying son I think: these are the times I'm going to remember when he graduates, gets married and has a family of his own.
If you really get stressed out with the crying and sleeplessness, just take some video or pictures being "cranky". That's what I did. It became a significant stress reliever.