there's no legal limit, but after five they stop giving any priority to the paperwork, unless you have some kind of real clout which we don't.
Mongolia doesn't limit but once you are over your US limit its more likely when the kids are grown they will go to Russia. One of the things about adopting in Mongolia is again the land is a little thin and they will do the best job possible of raising exportable people who can function in the world, but the resources for people who are going to remain there are for the ones who can't get foreign attention, so if you forget you adopted anybody when you were on vacation or something, you might one day find some rather grumpy people showing up in your neighborhood.
Though you wont get any calls from Mongolia asking for plane tickets.
*also if they didn't let the fertile people run with their will the race would die out and a lot of older couples, or people who send their own kids out to the general population then don't couple up till after the fertile years are over sometimes take in fosters for various formative experiences or longer so its not like we are all a bunch of irresponsible sluts or something, though sometimes in the modern infiltration the kids start to wonder that*
