Children need only be able to count to 12 to tackle this problem, particularly if they have some counters, sticks, blocks or some other material to model the groups of legs. Very young children would benefit from having the little story told while watching the legs of some toy animals just visible below a screen. Having some sets of plastic zoo or farm animals to experiment with, will help children having difficulty.  Leave them to try it individually and you just might be surprised!
 

 
Older children will soon realise that there's more than one solution. More able children should be encouraged to find all possible solutions and explain why they are sure they have found them all.
 

 
This is an excellent problem for children of all ages to record on paper and share with the class. Just encourage the children to think of a way to show how they arrived at their solution. It will be interesting for you to see which children choose pictures, numbers and operations signs and how they combine them.
 

 
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