I never had my sons wear them as toddlers since they were always with me.  What I did do though (and still do with even my older son with CAH) was to attach their medic alert bracelet to the front bucket of their carseats (or seatbelt).  That way in case of an accident and I was knocked out, a paramedic certainly could not miss it since they would need to unbuckle my sons. 

Oh, yes, and I also carry the medic alert card in my wallet right next to my drivers license.  Since it is common pratice to search a wallet for ID in case of an accident they would certainly find it.