We started on a three dose regime but changed to a am and pm system when our son was about two. Those doses were evenly split and we did not get the ratio right until he was about 3.5. You will not have this problem because he was also on medication for epilespy which made it difficult to determine a true picture of his day. The best advise I can give is to buy a small dairy and keep a history of your daughters day. Jot down her moods, energy levels, etc. By the time you have have her next blood test any pattern that may be there can be picked up. It worked for us because it was clear to see that the am dose was not high enough to get Liam to his pm dose on an even keel. He now gets a 3/4 dose in the am and 1/4 dose in the pm. He has not looked back since and five years on everything is scaringly routine. Today he came upstairs and asked if he could take his medicine on his own!! He did, (he thinks!!)so it does get easier once the levels are sorted and our kids cope amazingly well. Crush the tablets into some fromage frais which is better that yogurt because it is quite thick. If your tablets are 10mg each I would guess the dosage levels will actually come down initially given her age and size. Someone else on tablets who has a 21 month old daughter may be able to give you a ball park figure but her final level will be her own. Remember, you are supposed to be nervous and scared, but it will get easier. As you can see I tend to waffle on, but I hope it is helpful to you in some way. Shaun P.