Hi
They are getting older why don't you get them some grit. Ask your feed store which size is appropriate.
Sand is too small for them. It will just pass on thru the digestive system. Classic chick grit ( 1 thru 3 weeks )
is too small for them too. There is a next size ( 4 thru 7 weeks ) which is inbetween chick and adult grit
( 8 weeks thru adult). I believe Gran-I-grit ( made and sold by North Carolina Granite Co.) calls
chick grit "starter", the in-between size "grower" , the adult size "developer". The idea behind feeding poultry
the proper size grit at the proper times as they grow is to help them grow a healthier and larger gizzard.
When the females are grown, this better gizzard helps them do a better job processing the food for digestion.
This can result in up to a 20% increase in egg prdution.
Best,
Karen and the Light Sussex
in western PA, USA