I don't know if this is an option but could you offer to watch his nieces and nephews for a few days to give the parents a break? Make sure he does the majority of the work so he sees what he's wanting to get into.

I have a GF that did that and 20 years later still no kids lol. She always liked babysitting but just having 3 kids with her for 48 hours did her in.

Good luck to you