I wouldn't worry too much if they don't eat the alfalfa, so long as they are eating good quality alfalfa based pellets. I don't agree with tunes saying alfalfa shouldn't be given to kits though, but timothy should be the primary hay, with some alfalfa added. They need the timothy for their teeth, the alfalfa doesn't really do much for that since it's a softer plant, but it does contain a lot more nutrients, but if they are eating their pellets they shouldn't be lacking. I have never heard of a young kit getting kidney stones from eating alfalfa, but I have heard of some adults getting them from too much alfalfa since they don't need the extra calcium and protein once they stop growing. I've also not heard of kits getting diarrhea from eating alfalfa either, unless it's given suddenly. It's commonly suggested to give young kits (along with mother chins so the kits are introduced to it as soon as they start eating hay) unlimited pellets along with timothy and alfalfa hay until 6 months old.
I'm a bit surprised they don't like the alfalfa though, maybe a bad batch? Most chins seem to prefer alfalfa over grass hay. Do you know if they were being fed alfalfa before you got them? You can also try alfalfa cubes and see if they like those better.