As a TA (male) in an infant school I ran lunchtime recorder clubs for ten years, starting in Yr2; if children wanted to continue at the junior school, I also supported that while the interest was there. I was quite touched when some Yr6 children who had given up recorder some years before, asked me to coach them to play at the Yr6 leavers' performance. I had no recorder experience when I started, though I did play drums and keyboard. It is easy enough to teach yourself recorder from tutor books, then just keep a page or two ahead of the kids!
I coached Yr2 children to play percussion to accompany the Christmas performance each year. I also taught touch-typing to a few Yr2 children, but I chose pupils I knew would have the motivation and discipline to keep it up for a few weeks.
Twenty years ago I ran various computer clubs, but computers were fairly new then and more of a novelty. Today they are so common, it would need a very stimulating activity to engage the children. The Raspberry Pi £25 computer is being used in some schools to teach programming, but that needs some specialist knowledge. (A few weeks ago the millionth Raspberry Pi was made at the Sony factory in South Wales.)
When Yr2 finished SATs one year, the teachers let me have small groups from the two classes, and we spent about four weeks building a 2m tall tyrannosaurus Rex, from cardboard boxes the children brought in from home. We planned it from a picture in a dinosaur book, and as work proceeded the children took it round the other classes, explaining what we were doing. I was very impressed by the co-operation and involvement the children gave to the project. His 'nostrils' had black plastic bin bag linings, so felt quite cold and clammy. The tongue was layers of bubble-wrap, with PVA glue mixed in with the red paint, so it would adhere to the plastic. It was just glued in at the back of his mouth, so the front was free to be moved. Teeth were made from cones of white paper; start with circles, cut a line to the centre, then roll it round to the required size. (The Yr2 daughter of one of our TAs made all the teeth; she spent more time on Rex than any other child, and if her Mum couldn't find her at 'home time' she would come to the craft room, and she was usually there.)
At another school I did gardening activities with Yr6 (you would never believe how excited some children become seeing a worm; one of the most excited girls went on to read Law at university!)
Also at that school I had an after-school keyboard club; the children brought in their own keyboards, and I encouraged them to improvise and 'compose'. We also hooked up keyboards to the school's Clavinova, and to 'sequencers' (in the early days of digital recording.) All those kind of things can now be done via computers of course, and there are on-line recording studios and synthesizers, etc.
You have had plenty of ideas from other people, but consider what your own particular interests and skills are, and try and incorporate them.