For a party for kids and adults, I just finished carbing 5gal of rootbeer.
1.5 bottles Zatarain's rootbeer extract (order from their site.. $1.80 per)
2 lbs RAW sugar (better than processed sugar or corn syrup)
1 lbs light brown sugar
5 gallons water
Put in the keg, cooled, carbed and served at 15psi w/ 8' of line and a party tap.
Really good! But I do like strong rootbeer flavor.