A colleague's daughter behaved abominably, throughout the entire Girl Scout cookie buying process. Bossy, ungrateful, generally rude. This year, when she came around again, I checked a clock, declared myself "late for a meeting," and took off. I bought through my parish, instead, and the mothers and daughters have all been very professional and polite.
You could be "late for a meeting," too, if the wee ones persist in trying to make you buy things, if you don't want to say, "No, and you need to learn to take 'No' for an answer."