blueberry combing with conditioner or a special lotion takes a long time. If you comb thoroughly you remove the live lice so the children can't re-infect each other.
Like you said, anything you use needs to be repeated and it's the repeated thorough combing which removes the new head lice. We tried lots of potions before coming to this conclusion as my DD was in a class for years with a child whose mother refused to treat her. Whatever we used we were still combing out some live lice. We even experimented by keeping some in a jar and they lived for several days.
It would be much better for all concerned if people could get their head round the fact that combing and conditioning should be done once a week anyway to check their children's heads. It then becomes part of the normal routine, reduces the level of infestation when it is discovered and prevents transmission to friends and family. Much better for all concerned and a great deal cheaper than buying special lotions which you still have to comb through several times anyway.
If your child gets head lice
Day 1 - comb the head thoroughly in sections removing all the live lice and as many eggs as you can see. The eggs you should be concerned about are the darker coloured oval shapes near the root. The white ones are empty shells.
Day 3 - repeat sectioning and thorough combing with conditioner and _a decent nit comb.
Day 6 - repeat and continue for at least another ten days.
By this time you should only be removing new hatchlings. If you get them all before they have chance to reproduce you will have solved the problem.
If you're combing thoroughly you'll be removing any that are large enough to move to another head so they won't infect other children.
The eggs take a week or more to hatch then another ten days or so to become mature enough to lay eggs of their own. If you catch them in that time you have broken the cycle.
After that comb and condition once a week, checking for new lice. If you catch them early they will be much easier to deal with.
If you stick lotion on and assume it has worked it may well not have killed the eggs which are pretty resilient and when they hatch a new infestation will start. It will take a few weeks for the infestation to become bad enough for you to notice again by which time you'll assume it was a new infestation and by the lotion again.
More information on the NHS Choices Website.