Most children are smaller than we are. It is a good idea to get down on their level to share Christ instead of looking or talking down at them. A child doesn't want to be looking up and seeing our nose hairs while we are talking to them.
Many times we can relate better if we neel down or sit on the floor while we are talking to the kids. This will put us on a more equal setting, and they may hear more of what we have to say.
Hint... Try to neel or sit while talking to someone in a wheel chair as well. They may get a sore neck by having to look up to you all the time.