I don't weigh kits routinely, but those weights sound okay to me. The major growth spurt seems to come later on.
Your hay may be too light in protein. I feed an alfalfa hay for the most part. Grass hay is excellent for GI tract health and for satisfying the nibbling urge so that rabbits don't overeat on concentrates, but it is quite low in protein. If you can't get alfalfa hay, how about a hay with a good clover content?
Comfrey is an interesting possibility for adding protein. There is a certain amount of controversy about its routine use, but it has been used for a long time as animal feed. You might want to read up on it and get some plants started come spring. It is a perennial and can be invasive in some areas... not a bad thing if you are using it as feed.