Buy a nitcomb from Boots (personally I prefer the really cheap plastic ones, others swear by the more expensive metal ones), loads of bog-standard conditioner, and a little bottle of tea-tree oil.
Put 5-10 drops of teatree oil in the shampoo bottles - yours and the children's - and also in the conditioner bottles. Using this will help reduce the likelihood of the rest of the family catching headlice.
For treatment: the best treatment is wetcombing. Wash his hair, towel-dry, slather liberally with the tea-treeted conditioner and comb through with regular comb. Now split into sections and draw the nitcomb through it from the roots to the end. One stroke, do not go over again until you have cleaned the comb. I find that the best way is to have the basin full of hot water and swish the comb in it. That way you can see the lice as you comb them out.
Go over the whole of his head this way. Rinse out and refill the basin, and comb again - if he will tolerate it. I try to repeat until I'm not pulling out any more lice. Then rinse off the rest of the conditioner.
Repeat every 2-3 days for at least 2 weeks until you have had at least 2 clear combings. It is rarely possible to remove the eggs as they stick fast to the hairs, so you have to keep combing until they have all hatched. I think it takes about a week before the hatchlings start laying eggs, which is why you have to comb them out before they mature.
And don't forget to comb everyone in the family, preferably within the same 24h period, so that you don't reinfest each other.