Be careful of the parakeet grit as most of them contain calcium which your chicks do not need at this age. I got some builders' sand and it had all kinds of different sized grit in it. Sand works well as does natural, unpainted aquarium gravel.
I started my chicks on treats young as well; alfalfa hanging so they had to jump and then crickets from the pet store. It's lots of fun to watch the chicks chase crickets! But I also gave them sand for grit.
I would wet down their food first to encourage them eat their fill because sometimes when you first put the sand in there, they'll just eat and eat and eat it.
Mary