Yes, if I am correct in assuming these pullets are only just starting to lay. It can take a few weeks to get into the swing of egg production and when they are young, you can get eggs like this.
When you say mixed grit, is it something with calcium in it, like oyster shell? or sometimes called shell grit? This is important for them to get the calcium for the egg shells. They should eat as much of it as they wish, as they know when they need it.
If they have a source of calcium as well as a good feed mix (which will have calcium too) then it should stop after the first month or two of laying.
Let us know if it keeps up longer than that. I had one girl keep doing it and I give her a liquid supplement of trace elements and amino acids, as well as a liquid calcium supplement. But that was only because she was still doing it about once a week after four months of laying. Hopefully, you won't need to bother with that.
Good luck - and congratulations on your first chickens, they are so lovely to have around!
