looking for movie possibly in the 60’s or 70’s, very sad one

Hi to all, I’ll make it quick, here’s my question:

When I was young, I used to watch this movie with my parents (I’d say around the 80’s) but can’t find the title anymore, I believe it could be “The Champ” or “The Champion” but the story was not about a boxer, at least not the main one the pops up on search sites . I recall the story being this little boy with his dad on a boat and then something happened (bomb or a blast of some kind) and the boy got sick (probably cancer) and as the movie goes, the kid gets sicker and sicker and his dad is doing everything for him. I also recall his dad fighting with a bear or a tiger and at the end, right before christmas, the poor little boy dies. The boy’s mom was there too but don’t remember any of her interactions with him, nothing that struck me at this time

I know it’s not much but this is all I can remember
Thanks for your help on this!