We bought pens for our men three year old son, so that he can paint his little table. The review by Mr Koch, we can connect us in full here. By "design flaw" bezgl. The cap had already become useless the first 3 pins after one hour. The rest then stopped just another 24 hours. It should be made clear zumindenst age indication. Children from 3 to 6 are in my opinion, clearly overwhelmed with a sensible handling. We now have ordered from marking pens. These are much better!