I have 3 chickens, but in the Winter and Spring, 2 or 3 pigeons come into our backyard and 'hang out' with them. I just feed the pigeons normal bird seed for parrots and small birds. The chooks sometimes eat it too.
I would say that medicated chick starter should be ok for them as long as they don't eat too much. If you are worried, you could always save the food for later, if you want more baby chooks.