to avoid lice infestation, or at least keep it to a minimum, invest in a Nitty Gritty comb before your child starts nursery or school.
if you have a child with long hair, make sure they wear it tied up for nursery or school - plaited bunches are good.
cover their hair in cheap conditioner at least once a week and comb through with the Nitty Gritty comb.
keep a bottle of BizNiz to get rid of them if they should darken your doorstep.
personally, lice don't bother me. the thought of their bringing home threadworms is what really grosses me out.