Explaining what a stutter is to a child.

Explaining what a stutter is to a child. Hi guys. I just started a new job working with children under 15. I have a stutter, I would rate it about 5/10 (higher if I'm nervous). Some of the children laugh a little when I stutter (not to be mean I think, more like not understanding) some ask why I talk like that, one asked if I'm a robot because I'm 'glitching' (that's a new one). My question is how do I explain it to a child or anyone even? When people usually ask, I just say 'oh it just happens. I get stuck words sometimes. Don't worry'. I had considered asking my boss for advice but they haven't acknowledged it either and it would be a little awkward now. Thinking more about it I noticed I don't really know why I stutter or how to really explain it to anyone -adults and children.