Nine to twelve is the age of taking things seriously: a long build, a coding kit, a strategy game, a craft that produces something worth keeping. Kids this age notice when a toy is babyish, and they also notice when it is a phone in disguise. The toys that hold up respect their attention span and give them something to show for it.
How we choose for 9–12: from public award lists and reviews we keep kits and games with real depth, that can be done independently, and that don't push a child toward a screen or an account. We prefer things that are still interesting at thirteen. Every toy is checked against the CPSC recall database every night.
Before you buy: for coding and electronics kits, check what the kit needs that isn't in the box (a tablet, a specific operating system, an account). For chemistry and science sets, look at the age grade and whether adult supervision is required, and read the safety sheet before the first session.