i know its long time ago but i stubled over that because i like riddles...
ashmon is right
the kids are 2, 6 and 6
two are twins

the number over the door says 26 thats why the man thinks its not enough information... he's confused he thinks there should be 3 numbers but two kids are the same age
for us the barkeeper says the "youngest", so we know its not 3,3 and 8