Basing your life choices on random video clips seems to me to be inadvisable, criminally negligent, paralyzingly stupid, or exceedingly clever. Each situation requires a modicum of judgement as to whether or not you should emulate what you’ve seen.
You saw a video of a little kid teaching you how to perform a magic trick with a deck of cards, colorful bandana, or bit of string? Go ahead and have your child give it a try. Saw a video of a one-armed guy named Lefty teaching you how to perform a trick with a full gas can, razor blade, and blowtorch? You might want to think twice before you decide to proceed.
Do you really think that is acceptable to for a toddler to breath compressed air at any depth? If you have even the most rudimentary understanding of SCUBA diving, or of children why would you even have to ask?
Oops. I was typing my initial reply when the OP clarified his initial post. I had my son in a pool when he was about a month old, and water-play was an almost daily part of our lives. He was drown-proofed before he could walk, and while still a toddler he could swim to the bottom of a 10’ deep pool to retrieve my watch, then ascend and swim the length of the pool. I was ALWAYS with him, and never tried to push or cajole him to do anything he did not wish or have the capability to do, and insured that it was always fun for him.