In my minds eye this is from the CBS CFF.

As I remember the little boy was hiding from his family in the water under a dock. Quite sometime later he is found but his legs have completely seized up. They take him home and lay him out on a table and manually push his knees down to straighten out his legs. This causes him to scream out in pain.

Sound familiar? Thanks for any help.

I already answered privately, but just in case anyone else wondered about this:

The film in question is "Jumping Over Puddles (Again)". The two incidents you remember (hiding in the water, having his legs pushed down) are separate and unrelated. He's hiding because one of the stable hands is after him due to his mischief. Later he is suffering from polio, and part of his treatment is to have his legs straightened by holding them down. The boy eventually has to go away to a hospital for treatment.