@chrisburton loves Kirby like I love Arch :) He’s got his reasons and I have mine. For a lot of projects, it is my personal opinion that a CMS is way, way overkill. For projects this small, they will come with a huge performance overhead as well as security risks that you don’t really need… all so that clients can change they’re own site.
Now, @chrisburton is right in suggesting something like Kirby. There is no database with Kirby, so you’ve eliminated that layer of complexity… which is great.
But, I have to ask, why not just roll with static sites for these folks? They’re fast, simple and you make more money in maintenance/revision work. Just a thought.
If you’re going to go with anything… I’d go with something in the ilk of Kirby/Ghost/Jekyll. Although, the last of the three probably won’t solve the problem of clients being able to do it.