In reply to linnit:
As mentioned, finding a wall in your area and booking a beginners' course sounds like the best/easiest option especially given the weather, at least until you decide it's something you both want to get into. It's also the cheapest option usually as equipment hire is included and for sure I wouldn't start buying anything until I've done a few sessions...
You'd have to ask regarding your son obviously but I've seen A LOT younger kids at the wall that I climb so I don't think it should be a problem - you'll definitely be asked to sign for him as his guardian etc but those are all legalities.
Hope you both really enjoy it - let us know how it goes!