Only if one of those neighbors gets salmonella and e-coli from the unwashed lemons the kids used.
While it sounds cute and innocent, the fact is that people always did get more than then bargained for when kids use the potty and don't wash up well. Maybe that's your idea of fun, but its not mine.
Maybe its because my family owned a restaurant, but I have always known how chancy food is, and how you have to be very clean and very careful about what you take in.
You look at it from the standpoint of 'Oh its just kids" and I see dirty hands.
I don't think they should be fined, but they shouldn't do it. Sell crayon pictures, or bottled water.