Pretty much Qualatex or Bellatex are going to be your best bet in buying balloons - They are the current standard.
As for telling a kid no - it's just that. Explain to them that they can only have one balloon or you wont have enough balloons to make everyone a balloon creation.
Pops are a different story on occassion. If they are intentionally popping balloons then they absolutely get no more balloons. If, on the other hand, they get a bad break and the balloon pops - I'll either repair it or replace it if I can.
__________________ “Listen to the mustn'ts, child. Listen to the don'ts. Listen to the shouldn'ts, the impossibles, the won'ts. Listen to the never haves, then listen close to me... Anything can happen, child. Anything can be.” - Shel Silverstein
WOOHOO!!! You go, CheckerZ!!! Congrats on a successful party.
I agree that kids who accidentally pop their balloons should get a replacement. Often the balloons pop if they touch the grass. If it's an outdoor party and that's what happened, maybe suggest that they try a balloon hat that won't fall to the ground or a parrot that can rest on their shoulder.
I will replace a popped balloon after everyone has had one. But I replace it with the same thing they had before. They are cagey enough to pop it to get a different one if they see one they like better. That does not work for me. Most the time it just popped. I say it was under warrenty.