I’m not so sure about this. I’m not certain what did make me happy or unhappy. I have some theories and sometimes are really confident, but it’s hard to tell a year later out of all the things done which positively contributed and which didn’t.
Also, I don’t think the goal of parenting is happiness. Not for the parents or kids. Life is more than just being happy and I think it’s reductionist to focus on that as the paramount outcome. Especially to kids where there’s lots of stuff happening that may not pay off until years later- studying, being creative, training, learning, etc. Maybe positive decisions are not going to yield happiness for a long time.
And as a parent, there’s so much sacrifice that we make for kids that don’t involve any happiness for the parent but give more probability of success for our children.
We must remember that kids are very inexperienced in life, sometimes it is necessary to state this obvious fact. Parents have to make decisions for our kids based on how much life-experience they have. I don't let my 3 year old decide what to have for dinner, because it would cause him to be sick very quickly. We can bring this full circle to the OP: We don't let our kids have their own smartphones before they reach their teens, and I think that is wise.