The last and less desirable reason for a slow flushing toilet is an obstruction. Most of the time when a toilet clogs it is due to the volume that is going through the trap. Other times, something may get dropped in the toilet that won't go through the trap, this will cause the toilet to clog.
There are three articles that discuss 'Toilet Clogs'. See 'How To Unclog a Toilet', 'Plunging a Toilet' and 'Using a Toilet Auger'. Just about any type of obstruction can be dealt with using the information in these articles.
Children are great and well worth the few problems that they create. Sometimes, not likely the fault of the children, things get thrown in the toilet that shouldn't be there. Toothbrushes, small toys and other objects can get caught in the trap.
How To Remove Objects
When objects get caught in the trap, the toilet still works, but poorly. The obstruction will catch things that go by, slowing down the operation of the toilet. The solution is to get rid of the obstruction.
A toilet auger is the best tool to use when you have this problem. The problem will likely get worse and the clogs will become more frequent. In time the plunger will no longer work and something will have to be done. A slow flushing toilet has now become a clogged toilet.
Using a Toilet Auger or Snake on a Toilet
A toilet snake is an oddly shaped device that has a short section of metal snake that goes through it. It has a hand crank and the snake portion is just long enough to get through the trap on the toilet. Since most objects get caught in the trap, the auger works very well.
See the article, 'Unclogging a Toilet With a Snake' for instructions on how to do it and where to obtain an auger.