The first solutions we rceived seemed to focus on getting $3, 4$ and $5$ plants in the different areas while sharing one. Perhaps we made it look as though there was some calulating to do.
To achieve solutions for the three children getting $5, 6$ and $7$ using just $10$ plants, the most successful solutions were practical. Kagan at St. Michael's Sandhurst used buttons in circles to show a good example of a correct solution - well done, and here it is.