We have these at our toddler group and they are brilliant. They do go a long way and keep well. Value is good compared to what you get in Tesco, it actually covers really well. You can water it down for string painting or straw blowing :)
Easy peasy to wash out, DD got black on a light cardi, came out no problems. Washes off easily with soap and water.
We used it with babies and upwards for handprints recently for Mother's Day craft, obviously you don't want them to eat it, but the odd lick is fine.
You can also buy this in powder form you mix with water (tempura paint), my stash has been handed down to me by my MiL who ran the play group I attended as a preschooler (and I'm 32 this year!). As long as it's stored well it is still good for years (decades).