Best martial arts for 4/5 year old?

[DGGR]

I'm thinking of enrolling my 4 nearly 5 year old into a martial arts class. To help him get over the urge to play fight and encourage discipline with it.
My father always did judo. I tried it and hated it because I just wasn't competitive enough and wanted to chat the whole time.
My brother in law has just started jiu jitsu too and loves it.
I like the idea of these because there's no striking.
But, I have a problem with head injuries. DS 1 has had some really nasty head bumps over the years and I'm paranoid about him getting any more and it causing damage.
Can anyone recommend a good martial arts discipline not only for a young boy but also an anxious parent 🤪
Thanks

My daughter started Shotokan Karate at 4.5 and it's all about controlled contact, controlling your movements, strength and neatness. They wear mitts and pads for sparring, but it's all about the movement not the hardness of the strike.

My kids do judo. I have one very competitive 11 year old who fights at national and international competitions and a 7 year old who isn't competitive at all. The 7 year old is clumsy so even just learning to fall without sustaining injury is useful. The main thing is finding something they enjoy and will stick at. Judo will be a lot more contact but at that age it will just be a bit of rough and tumble and learning the fundamentals of the sport. It goes up a notch at the age of 8. If they don't have much of an attention span I would go judo over karate