It's a rule at most barns I know of that giving treats inside a paddock or at a fence line is also a huge no-no. I've seen a few fights break out over the years when there's a kid with a handful of tasty treats and the competition begins. If not a fight, there's often pushing and shoving.
Yes, an experienced handler/owner can lessen the chances that there will ever be a problem in this situation, but IMHO, never completely rule it out...and a less than perfectly educated handler (AKA, most kids) can end up getting hurt in a scuffle, or simply pushed and possibly trampled if they go down.
I have a personal rule to never treat inside a paddock at all. A side effect is that the horses are usually well mannered coming out of the paddock because they equate the other size of the gate with the point the treats may start flowing. ;)