do you mean take them outside to eat grass or put grass in their cage to eat? i let my baby have some 2 weeks after she weaned to see what she thought of it,didnt let her have much though
I wont let them out on grass til they're around 6 weeks, atleast.
There are too many things rabbits can get that are not treatable, and I like to keep that minimized until I feel my babies have an established immune system.
If the mother was fed grass during the pregnancy, then I'll let the kits nibble on grass at about 4 weeks of age...but they don't get a huge handful or as much as they like - it's really just a taste.
I still follow the "no-grass-until-6-months" rule with most of my juniors though, just to err on the side of caution.
It's just better to be safe than sorry. I wouldn't let any babies whose mothers didn't get grass during the pregnancy nibble on grass at all.
I've let mine out into an x-pen at 3 weeks with momma, but when the babies are a week old i start letting momma out in the x-pen to nibble grass, as she hadn't been able to get out on it for 2 weeks(week prior to due date to week old kits) and they usually love it- though they are more apt to run and binky than nibble the grass the first few times. I only leave them out with her for 5 minutes.
I dont allow my buns to eat greens of anykind till around 4-6 months, depending (they have never tried to eat "lawn grass", just arent interested in eating it I guess).
Now, just to go out and play "in" the grass, around 6-8 weeks in a secured run is good IMO.