Welcome to the forum!

Please read the Pacman care sheet. It should help you with some of your questons. Often times it is better to keep the babies in a smaller enclosure and then move them to the 10 gallon when they get bigger. Sometimes large spaces make them stressed. Also, the larger the space the harder it is for them to catch their food. Although if you can get him/her to tong feed that shouldn't be a problem. What sized worms are you feeding him? Are you using a vitamin supplement and calcium powder with D3? Are you de-chlorinating the water?
Frog Forum - Pacman and Horned Frogs - Ceratophrys - Care and Breeding

Also, these videos on tong feeding should help you:
http://www.frogforum.net/pacman-frog...-froglets.html
http://www.frogforum.net/pacman-frog...ing-102-a.html
Some frogs will take from tongs immediately, some take longer to learn, and others refuse to eat from tongs. It varies from frog to frog. Try offering different food items. If it is something they really like, they will be more likely to take the food from tongs. I also find it helpful to offer food from tongs first; if they won't accept it, I drop the food in front of them with the tongs. Eventually they make the connection that tongs bring food.

Please post pictures of your frog and set up. If you have any other questions just ask.