Children can see ghost and a number of other things we can't and here is why. There's a biological theory that's actually quite convincing! Adult humans can only see 400nm - 700 nm on the electromagnetic spectrum. UVA light falls just below visible light at 400 – 315 nm (anometers). Infrared light falls just above at 750nm – 1mm. So in layman’s terms, that means that what you are able to see of this world is quite limited - there are a lot of things happening just outside your vision that you'll never witness.
Should you be worried about it? In most cases, no. However, you should keep a close eye on your child and watch for behavioral changes, especially if the changes are negative.
In the videos below; Watch, "Baby Girl Talking to Spirit”, at the 57 second mark, you will see an orb drop down and move off to the right of the video.