You need to take them to visit someone with a home or garage workshop with robot experiments..this will grab their attention...However never leave kids alone with adults unless close relatives.
I had a line follower robot kit called Movit. Everything needs to be assembled right in order for it to work. The photosensor head must be snug to the floor.
It's a reply for 1-month inactive thread, and does not meet the child age group originally mentioned (actually it seems not that simple), but the feature set of this toy is really amazing.