I did the same as a kid, I loved being underwater. I think a good indicator if a kid is doing that for fun or drowning is that when I would do it I would usually launch myself out of the water, take a really big overexaggerated gasp and then go back under by pointing my head down and doing a sort of
1
0
0
dive maneuver. I would also be giggling and doing flips and handstands so that probably helped.

On the other hand usually people who are drowning are doing so because they can't keep themselves afloat so they'll barely come up and then sink back down instead of my launching myself back underwater.
1
0
1
Obviously take all this with a grain of salt, I have taken swimming lessons and can swim quite well but I am by no means a swimming instructor or lifeguard. So if anyone with more experience/knowledge wants to correct me please do so!
1
0
0