Will my 3 week old pups get sick if I have to switch their Mom's food for a couple of days?

Mom is on Science Diet puppy and we ran out and we can't get it till Monday. She's on hard mixed with some canned. In the meantime, we were going to give her Purina puppy, is that okay? Also, I gave the 4 pups a teaspoon of canned pup food to try and they ate it, is it too young to introduce? They do have teeth. They are technically 3 weeks and 4 days old. I was going to introduce water at 4 weeks and moistened hard food with a teeny amount of canned 'cause I really don't like soft food.