do you need a motercycle licance to ride a pocket bike.
In the UK you would need a licence and insurance to ride it on the public highway, but it will be a moot point as the pocket bike will almost certainly not be road legal.
Just in case you were thinking otherwise, it is unlawful, irresponsible (children and all that) and extremely antisocial to use one of these things anywhere other than on private land with the owners permission. You must not use them on public land, bridle paths, round the park, pavements etc.
Best burned, crushed or otherwise destroyed with extreme prejudice in my experience.
You don't need any sort of licence to ride one on private land.
If you wanted to take it on the road, then any licencing requirements would be academic, as Mungecrundle said, as you almost certainly wouldn't be able to make it road legal in the first place.
I had one for a while (a present - long story) and it was a bit of fun to ride around, but with no suspension and your knees round your ears, they get uncomfortable pretty quickly. Most of them are pretty basic, cheap Chinese import rubbish with unreliable brakes and dodgy engines - mine had a habit of overheating and refusing to run again until it cooled down (once it eventually started in the first place).
Eventually sold it to a lad whose parents owned a farm, so plenty of space to ride it.
If you really want to have a go on one, have a look for your nearest karting circuit that has them. A friend of mine did this for a birthday - sadly, I had prior commitments elsewhere that I couldn't get out of.