Well they lived on the yolk in the egg so why would that be wrong if the egg is not an embryo.. It is just an egg. Calves drink milk....
Remember even a fertilized egg is not a chick embryo until it is placed in the incubator or under a broody hen and heat is applied. Eggs are great for chicks - scrambled or hardboiled is best so they don't want to eat their raw eggs when they lay them.
As for treats - yogurt with chick crumbles on top is always a fav
Meal worms
Spaghetti noodles (cooked)
10 days is kind of young for treats I would wait another week at least. You want them eating their chick feed and not filling up on "junk" food. Just kidding - chickens are natural foragers anyway. They love almost everything - except mine will not eat broccoli
Caroline