Well I'm not sure that metal detecting is a bad thing per se. After all, so many of the amazing objects you see in the british museum and the like have no doubt been found that way. Waving a metal detector around a field where you've asked permission to be there doing it, and hearing a beeping, and scraping down through the soil to see something from the past - that'd be pretty cool. And if you then call someone professional in to excavate it carefully, and altruistically share the information gleaned with your fellow members of society, and maybe even resist the urge to charge the local museum squillions of quid to buy it off you - I mean that sounds fine doesn't it. What doesn't sound fine is sneaking around places you're not supposed to be (middle of night optional), digging a huge hole to get out your treasure, not reporting you've found anything, putting it in a box in your shed for 40 years until you die whereupon your children chuck it in the bin. That's the problem people have with metal detecting I would think. In fact it's not a problem with metal detectING it's more a problem with a subset of metal detectorISTS who consider their private excitement more important than anything else. Some of them aren't very nice at all as I read recently on the Heritage action blog. So don't take my comment that I don't think your kid should have fun. I'm sure that in the event that he comes across the next staffordshire gold hoard, you'll advise him to report it after he's finished dancing about the field.