Most times on the shampoo the will be a company number to ask the age one can use these shampoos, when my kids had it I used Olive oil and let it sit on there for a while to soften it then picked it off with a tooth comb, I guess it sounds like you did similar thats when the question arises how to prevent it, well if it comes back, do it again, maybe at some stage it wont come back, have you thought to google 'cradle Cap" and see any ideas out there on prevention.