As we all know children do not have a great deal of patience. If you are planning on getting them involved in the garden make sure it is a task with a quick result in order to keep them engaged.  Involve their senses to keep them interested. Perhaps allowing them to have their own patch to incourage independence.  Learn to relax and let them get dirty and have some fun.  Check that the plants you have selected are safe for children, as some seeds can be poisonious while other plants can cause skin irritation.  Teach them  to never eat anything in the garden without you being there with them.