Is it ok for a boy who had a bone marrow transplant jan 2017 and who is still having infusions once a month to be at bday party public place eg: pools?

Best ask his docs: Without a full understanding of what his history, diagnosis, treatment and current status it's a bit much to expect a recommendation on his daily risk/needs. This is a question best directed to the treatment team that knows him well.

Depends : It depends how is his health and what medications ( immunosuppressants ) is he on . His oncologist would be the best person to answer this question.