Depends on all sorts! What colour is DS's hair? If it's brown then you might find the lice a bit difficult to spot, but see the cream/white eggs first. If (like my dc's) he's blonde you usually spot a moving louse first, or tiny little black baby ones clinging to a hair shaft. Sometimes you just happen to find one.
Keep combing, keep checking..and do yourself while you're at it!
Teeny tiny! Like grains of sand. The lice will probably blend in nicely with ginger hair! If you've not got one, get one of the nitty gritty combs from boots. They're about £10 but, sad to say you'll probably get your use out of it.
You often know your kids have nits when they start scratching. Behind the ears is a favourite spot. If you have an infestation, it will take a few weeks work to get rid of it. You can get various stuff to put on the hair but the least nasty way of getting rid of them is to wet comb the hair with conditioner on. I've never used Hedrin but apparently its good. Tea tree is supposed to help deter them too, use shampoo/conditioner or add a couple of drops of the oil to rinse water. One colleague kept nits at bay in his son by routinely combing his hair with a nit comb once a week, got rid of any stray bugs before they got chance to breed. Makes me itch just thinking about it. My DSC's got nits a lot.
If you're going for the combing method, then every 3 days (I think) is sufficient. Load of conditioner, comb and rinse. Although, after 8 years of nits, I'm more inclined to reach straight for the hedrin!