I have a chick who is a month old. He/she has wing feathers and tail feathers starting but not too many other feathers. Your babies are probably 4-6 weeks old based on what you've said. My Chickie loves live mealworms, grape, bread, etc. I have photos at
http://www.fishpondinfo.com/birds/chickphoto2.htm that show his/her progress as he/she ages (and also his/her father from two years ago).
Birds make two kinds of excretions. There's the regular dark poo and then there's the liquidy white stuff that is the equivalent of mammalian urine even though it's a white solid for the most part. In birds, it contains uric acid instead of urea in mammals. If there's a lot of liquid, the chick may be losing too much fluid. Be sure they have enough water. The problem could be related to diet, parasites, or other problems. It's hard to say. There are many reasons a mammal could have diarrhea and many reasons a bird could have extra liquid in their white excretions too. The white stuff comes from their kidneys so there could be a problem with them. Hopefully, it's something minor that will pass. I'm certainly not qualified to diagnose it. I'm not sure if a vet could figure it out. If they seem fine otherwise, I wouldn't worry too much.
Chicks will try to eat various things out of curiousity. As their adoptive "mother," you have to make sure they don't have access to things they shouldn't eat. If they eat fabrics, they could get stopped up, stop eating, and even die. Just like human and other mammalian children, chicken "children" want to get into trouble!
Good luck with them!