Every parenting group has a moment where someone asks about screens and the replies fill with numbers. Follow 3-6-9-12. We do the one-hour rule. Have you tried 20-20-20. The rules travel fast because they are easy to remember, which is not the same as being true.
Here is what the named rules actually say, where they come from, and which ones deserve a place on your fridge.
The one-hour guidance
The World Health Organization recommends no more than one hour of sedentary screen time a day for children aged 3 to 4, and says less is better. The American Academy of Pediatrics lands close by for ages 2 to 5: about an hour of good content, watched together when you can. These carry the most evidence, and both bodies say the same quiet thing underneath: what matters most is what the hour replaces.
3-6-9-12
A French psychiatrist, Serge Tisseron, proposed it as a set of doorways: no screens before 3, no personal console before 6, the internet only after 9 with an adult nearby, and social media after 12. It is a framework rather than a finding, but its first doorway agrees with the strongest research. The youngest brains gain the least from screens and lose the most conversation to them.
20-20-20
Every 20 minutes, look at something 20 feet away for 20 seconds. This one is about eyes, not development, and it is sensible for anyone who reads on a screen, including you.
The rules nobody can source
You will also meet the 3-3-3 rule and the 7-7-7 rule, which mean something different in every post that mentions them. When a rule has no stable meaning, treat it as a costume that folklore wears. You do not need it. The principles underneath every good rule fit in one sentence: less is better under five, together beats alone, and conversation is the thing screens quietly eat.
So pick the rule your family can actually keep. A rule kept loosely for a year beats a strict one abandoned by Thursday.
And if the hardest part is what fills the quiet after the screen goes off, that is the exact gap we built Lumi for: a screen-free friend that talks, tells stories, and asks your child questions back. The pre-order list is open, and joining costs nothing.
