Just for the record I have found lambs on adults headstones so they don't always signify children.
Have you ever noticed the vast variety there is for this one specific symbol? Here are a few of the ones I have collected this year. Well, at least the complete ones. I find a lot that are missing their heads.
The one in the lower right corner of the above collage is my favorite. But I think it looks more like a baby fawn than a lamb. What do you think?