Halacha: may one give a hair cut to his son before age 3 for medical reasons(eye infection, the boy scratches eyes when hair get in) and safety issue-wish to take him swimming and pools have powerful filtration/suction system and long hair may present a risk/Has veshoaom . Can one harm the soul of a child if his hair is cut before the age of 3? Thank you.
It is perfectly permitted to cut hair for good reasons, and many do so when hair gets into eyes and so on. This is the more so true where only part of the hair is being cut, and not a full haircut.
Some communities (especially some Hassidim) are very particular not to cut hair before the age of three, but this is not a full halachah but only custom, and where there is a need one can cut hair.
There is no harm to the soul of the child.
See Orchos Rabbeinu Vol. 1 p. 233 (see also Arugas Habosem, Orach Chaim 210, who writes that the haircut should not be given before three, but this will only apply to a full haircut, which involves the mitzvah of peos, and not to cutting part of the hair).