I think the prerequisites are:
- the child is able to make it. It all depends on the child. The minimum age in PADI is 10. Some kids will be more than ready at that age. Others will still be babies, or are too much all over the place to get the minimum of discipline that will avoid problems. Don't ask yourself if your child is ready. Ask others: their opinion will not be biaised...
- the child is begging for it. No child should ever dive to please his/her parents. It should be the parents giving up on saying no to their child.
- the parents are divers. That will help for explaining the theory. It will also make the child understand that diving is fun, but it has some risks that you should always keep in mind. And it allows both generations to share the experience.
- your child has tried a few times in a swimming pool, has breathed a few times on your octopus, and has made a couple of intro dives. If after all that he/she keeps asking for more, then have him/her certified. But pick a good center. I have seen centers advertising the Junior OW in 3 days. Forget it. Take at least 7-10 days, or have your child been through the book way in advance.
Once he/she is certified, I suggest few guidelines:
- 1 dive/day as an average
- be very strict on the depth limit
- let him/her write whatever he/she wants on the logbook. After a while, ask for reading it. If you are allowed, you will find it sointeresting. A completely different prospective from yours on diving.
The absolute DO NOT:
- don't even try before 8. The respiratory system is not ready at all, neither the mind. 10 is already a bare minimum.
- never let your child going underwater without an adult ( and one that you would choose as a buddy for yourself.)
Cheers.