Take care with your spelling. Improvisation - is used mostly in the context of music, when soloists play 'freely' around a basic music structure. People can also 'improvise' when they need to come up with a new way of solving a problem.

I think it's more of a case of context than a pattern. 'free play' would only be used in a context where it would be more normal to have structured play, or lessons. In most cases - that means school, or kindergarten, or possibly something like an organised event for children. So - 'After class, the children can have 1/2 an hour of free play to unwind'. 'The program includes several periods of free play time during the day'. 'free play often encourages creativity more that classes'. Children learn their own limits by pushing those limits during free play.