However Greenpeace is not very trustworthy according to many articles. It could be that Greenpeace are right, but it could also be that they want to confuse the public which makes the whole thing even more scary. Fact remains if it is easy to avoid it, try to avoid it. At least until we know more Organic Lead from plants is not poisonous. Planting herbs, sunflowers etc.
Small children use their mouth to measure the size of objects.
You cannot forbid a small child to do this. It is only natural. It is a necessary step in their development to put things in their mouth. Try to get hold of honest old fashioned toys made of unpainted wood or cloth or other alternative materials. Make sure everyone washes their hands before eating.