The article doesn’t give a clue how old these children were. Assuming they were quite young (as lemonade stand operators usually are), the caller may have been concerned that they were awfully young to be doing door-to-door sales without adult supervision.
I’m also wondering if this sales effort was purporting to be connected with the Alex’s Lemonade Stand charity, and the caller was wondering if it was legitimate. The late Alex Scott, founder of Alex’s Lemonade Stand, lived with her family just a couple of miles from Haverford (in Wynnewood), so Alex’s Lemonade Stand has been a big deal in this area for many years (before it went national).
All that is a matter for the lemonade vendors’ parents, not the cops, Mr. or Ms. Government Shrinker.