I was put on ADHD meds as a 4 (almost 5) year old after my first violin lesson, this was back in the mid-90s. My mom said it was the weirdest thing she'd ever seen: I so badly wanted to sit still and listen because I wanted to learn to play the violin but I literally physically could not do it and became visibly frustrated with myself. And a bad change in meds in 1st grade (because I didn't like the bitter tablets) was enough for my 1st grade teacher to contact my mom about my change in behavior. It was only as an adult that I realized this must have been the few days where I got in trouble and had to sit out during recess, which was humiliating to me. I have anecdotes for days about this kind of stuff.

I am eternally grateful my parents took me to a psychiatrist when they saw some aspect of my behavior wasn't normal and that it was affecting my quality of life, even if I was far too young to know or understand that. I think it was the humane thing to do, 100%.

People talk a lot about how terrible it is that 5 year olds are put on this shit, but extreme cases like mine are out there and they are legitimate. Sometimes things show up early because they're severe enough. It'd be fucked up if 10 year olds on SSRIs was the norm, but I have no doubt that there are rare cases where it'd almost be cruel /not/ to do it. Bipolar can absolutely be diagnosed in children. If you can diagnose it that early, why wouldn't you start treating it? Isn't that what you SHOULD do as a parent?