I started with my nieces and nephews when they were about 7 years old. At this point they have reached a mental level to comprehend and relate more of what you will tell them. There is some debate, but their skin should have developed to a point that they should not absorb lead through their skin. The debate is when that process occurs and I suppose it would have to do with the amount of exposure as well. Mental maturity will be up to you to judge of course. Kids definitely achieve mental maturity at different rates.