J.A.
Hi L.,
My son has been on synthroid since he was about 6 months old. For him his thyroid was working too hard to keep the numbers in the right range. He is on a very low dose and it really is no big deal. I give it to him with whatever he is eating for breakfast, or sneak it in with a few m&m's. He is now 5 and still a bundle of energy. I also have a friend whose daughter is about 14 who has been on it since birth.
Again, it has been no big deal for her. Good luck!