I have used paint a lot and the answer is how messy are you planning on getting. The easiest and safest are children's poster paints. The good ones are lovely and thick and vibrant and are safe for kids. Some do stain skin and clothing so beware (red especially). Next comes matt emulsion paint. Cheaper in quantity but is marginally less afe. It does wash off easily though. Next comes gloss paint. Once upon a time you wouldn't use it but now a lot of paints wash off reasonably easily with a good soap. I wouldn't suggest all over coverage. Finally there are enamel paints and these are a devil to wash off. I have used them all and if you want more info or pics let me know.
I've used poster paints suitable for schools use. You can easily buy it in bulk online. I used black and had no trouble with it staining my skin, hair or the enamel of the bathroom. If you have any doubts just test an inch for an hour. The only difficulty I had in clean-up was washing it out of the inside rim of my eyes, but it came out with a little gentle coaxing.
paint is for me the prefect substance in the last 15 years...
1. it makes a great mess 2. there are no sticky stones like you have with mud 3. it's compared to sirup, custard and so in the end chaper by the quantity you need 4. it feels smooth and silk 5. it stinks less than e.g. ketchup or cream in the end.
As mentioned before childrens poster paint is harmless.
But I prefer paint for indoor walls as it is thicker and smoother. As long as you stay with water based paint, there is no risk at all as long as you don't eat it or pour it into the eyes. All other is washable. If you want to colorize it maybe use green, black or blue less, as the skin might keep it for some days.
Love you, too
