Photographic License

You don't, but if you take pictures of children in public without express permission I think the police will occasionally lift people for behaving suspiciously. I believe the guideline is to be "sensitive". Technically, though, you can photograph anything you like in public.

In private, or when the child is acting as a model, though, the _child_ needs a licence if they are under 16 and are a "paid model". There's some information here, along with a bunch of stuff on releases and so on that you may need:

http://www.theimagefile.com/v/help/2008.html

I'm assuming from your profile you're in the UK.

Edit: Obviously "indecent" pictures aren't usually a great idea, but I'm sure you weren't going to do that...

yeah, im opening a studio in Dundee on Monday, and I only just realised that it might not be fully legal to get children in (with parents permission and accompaniment of course) and am kinda worrying about it now!

I won't be paying them, the parents will be paying me! HAHA

I might come up with some sort of form for parents to sign before I photograph their child or something like that...

Well obviously I'm no lawyer, but so long as you get the parent's consent I don't see a problem. Maybe worth getting the opinion of someone who already does something like this.

Hmm, you might have to fill out a disclosure form - I think anyone working with minors has to do one and get checked out. That's the case with filming at least, I'd guess that it would be the same for photography.