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This activity has been particularly created for the most able. (The pupils that you come across in many classrooms just once every few years.) It is seen as a possible follow on from More Children and Plants.
So, set yourself a challenge like;
"Distribute $15$ objects among four sets having $3$ in one, $4$ in another, $5$ in another and $6$ in the last."
Then take this further by having five sets with the extra set having just $1$ object.
You'll be able to think of your own examples too.
Perhaps most important is to formulate some generalisations that can tested.