Milk choices for 1.5 year old

my boy takes Breastmilk since born and reject all types of formula. he is going to child care soon so I wanna introduce him to other milk alternatives.. is UHT milk a good choice? what other choices do I have? I was told by the school that they serve Fernleaf. I am afraid my boy will refuse to drink.. I am worry that he doesnt get the proper nutrients in school... (he doesnt eat well on solid food too...)