If Momma were in the brooder with them, she would make a happy churrup like sound and let them know it is okay to eat it. With out the momma, you will have to just offer bits to them to see what they like and dislike - Yogurt is a good one with some crumbles in it. A little bit goes a long way. Crumbles make everything more inviting....I tease my daughter about sprinkling crumbles on her veggies! The chicks know the crumbles and that helps them to experience other things. Yours are kind of little still but they will double, triple and quadruple in size as the weeks go on and may enjoy treats. It really isn't necessary to give them treats now. They like red things best it seems. Watermelon is good treat. Small meal worms!
Caroline