Yep, oatmeal-type foods. I find it easiest to just use the instant baby cereals sold in pouches. I can keep it in the freezer so it stays fresh longer and just add hot water to a little as I need it, but then I only give it as a treat to a couple of adult hamsters. For the number of hungry mouths you'll be feeding you might want to start cooking it from scratch in larger batches!
As for protein-rich foods, mine always liked chicken or turkey. Baby foods in jars are good so long as there's no onion or garlic. The dinner-type ones containing meat, grain, and veg are good choices. Go for the ones meant for babies under 6 months, they're usually the ones that don't have the onion/garlic seasoning. I also just found out that they LOVE shrimp
Not sure if that's safe for babies though, I'd stick to what jemmalg listed
