I understand that it's very important to start your investment journey very early, at a young age which is an added advantage, but putting the exact amount they should be investing is what I didn't find ideal, because everyone don't have the same financial capacity, the way $10 might be very little for you, might be a very huge amount of money for some young lads out there, the best thing is for them to cut their coat according to their size, by investing what they can afford to do away with for a very long period of time, and we all know our level better than anyone else, so it's best to act according to our level financially.
But one thing am quite certain of is that if they can be very consistent in their accumulation, in ten years time or more, no matter how small they invest weekly or monthly, they would have accumulated a very good stash of Bitcoin if they are consistent in their accumulation.
It is good to start investing early but it is also good to think about how much money each person has. Saying that people should invest certain amount of money is not realistic and can be discouraging for those who do not have lot of money. Your idea to cut their coat according to their size is smart because it reminds people to only invest what they can afford and to think about their long term financial goals. With doing this people can make smart decisions that fit their own financial situations and goals.