the tooth moves slightly
the tooth moves a lot
the tooth goes back inside the socket
the tooth flies out(avulsion)
the tooth breaks(save the fragment in milk, water)
In any of the above cases, rush to your dentist. In case of an avulsion, you could simply rinse and put the tooth back in the socket. Do not scrub or it will kill the vital tissue(periodontal ligament) around it. If unable to do so, save the tooth in the mouth(if child is old enough to not swallow it), milk, coconut water or if none available, plain water and go to a nearby dentist as soon as possible so he may plant it back in.