Microsoft MakeCode
I ran a code club at my local primary school last year using the micro:bits. They're awesome little devices, super simple to get some pretty effective results with. I had 15 kids aged 7 - 11, some of whom were there only because they went along to every after school club it's cheaper for working parents than a childminder, and all of them absolutely loved it. We did some great little projects - making 'musical instruments' with speakers and the gyroscope, making those buzzy 'steady hand' games, sending messages to one another via bluetooth, etc...