Just a general rule I use, but perform almost no trimming until tree sapling reaches 4-6'. Perhaps if it was forking early I would trim back to one trunk at early stage. Aim for 10-15% foliage reduction as maximum, in no case more than 25%.

i would snip the bottom two branches.. every year ...

that is.. if i had any inclination to encourage free range elms...

do you have an ID on these... if they are siberian elms.. what a mess...

pic of plant.. and leaves will get you an ID.. to find out if you are even growing a worthwhile tree....

i mean really.. if you are going to invest a decade in growing a decent tree ..NOW is the time to find out if its a decent tree ...

i kill a couple thousand siberians every spring .... a horrible blight on humanity.. not to mention.. mother earth ....

ken