oh that brings back bad memories
When my youngest dd was less than a week old my ds and dd went camping with some family friends and came home with lice
I would definately check everyones head for nits (eggs) and lice - go outside if it is sunny or go under a bright light if it isn't - check around collars and behind ears - when I taught prek those were really easy places to find the buggers - they are totally obvious (imo) when you see them - use a very very fine comb (after brushing or combing out curls or knots) to carefully go through the hair (this was the best advice I was given) - if you have a ds and they do have lice I would suggest cutting their hair very very short (or buzzing it) - for girls that isn't so easy if they love their long(er) hair - if the nasty bugs are in the hair you can treat them w/o chemicals by using a mayonaise or tea tree oil hair mask and leaving it on for several hours. Not sure of anything else that would work and come out of the hair easily
The gal that used to cut our hair suggested doing a vinegar rinse on my kids hair after shampooing daily to prevent lice from attaching to the hair shaft/scalp whenever they went camping or were in a group care setting where lice may be present (school, childcare) .