Use a comb and loads of conditioner in the hair to get them out. But don't buy one of the standard combs - the one you want is a Nitty Gritty comb. They are expensive (around �9.99) but worth every penny as they get the eggs off the hair as well as taking out the lice. And remember to rinse the comb after every stroke through the hair.
If you want to try an essential oil mix, 2 drops each of Bergamot, Eucalyptus, Geranium and Lavender oil in 20 ml (4 teaspoons) of a carrier oil like almond oil. Massage it thoroughly into the hair and scalp, cover the head for several hours (overnight is possible) then wash out with a mild shampoo. Finally do the bit with the lice comb. Repeat at 48 hour intervals 3 or 4 times and that should get rid of the infestation.
As quizbag said, don't forget to wash things like pillowcases, bedding, coat collars, hoods, scarves and hats as well. If something can't be washed, a mix of those oils in alcohol (e.g. vodka) or surgical spirit can be used to sponge them instead - you want a mix of about 10% oils to the quantity of alcohol or surgical spirit.
Oh and tell the kids to stop doing the hug thing with their friends for a while. The hair-to-hair contact is one of the was the things spread.