There is only one way to get rid of lice and that is to break the cycle.
A single lice once hatched, takes between 7 to 10 days to reach maturity and is then able to start laying eggs. Eggs can take 7 to 10 days to hatch.
A mature lice can lay between 6-10 eggs a day.
Picksan, Nitagon and other lice shampoo's are all quite effective....follow the instructions, but then do it every second to third day for about 3 weeks. Combing with a lice comb also helps.
Ask the nursery not to brush your childs hair with a communal hairbrush and that they should tell other parents to treat their children too.
Lice, as taboo as it is, is actually VERY common in creche's and even in the primary and high schools because nobody wants to talk about it. the best thing you can do is to get into the habit of checking your childs hair regularly (and your own) and to not stop treating the hair until everyone in the family is clear.
also contrary to popular belief : lice LOVE clean hair
You should also wash all bedding and towels etc, and then tumble dry them as washing alone does not kill them.
Good luck!