This is a hard one to answer because when I was a child my dad gave me a fossil too (my first fossil) and he did not realy know what it was (i am now 56yo)
I can only tell you of an experiance that I had a few years ago when I purchased a similar fossil from a reputable dealer although my fossil was only one tooth.
It stood in my collection for a couple of years gathering dust so one day I decided to wash it, I turned the tap on and put it under the running water only for the matrix to disolve and be left with a real tooth, a seperate real root and a pile of matrix in the sink that had washed off.
Partial fake or complete fake made up of real parts you have done the rite thing in encouraging your kids to question anchent life.
I think it is made up.
These are not so much fakes but are more composite fossils, that is to say they are made from real teeth & bone but arranged to make them more appealing to most people .
These come from Morocco & although I'm no expert yours looks very much like a composite to me.
Also i should point out that these are not actually dinosaur teeth but are from a marine reptile called a Mosasaur, but i think their just as, if not more interesting. You still have a good display piece & i think its a very cool fossil for your son to marvel over & show his friends, providing he knows what it is & that a genuine piece like this is quite rare & would most likely cost several hundreds of pounds maybe more.
Heres a link to some very good information & photos of Mosasaur fossils & a lot more.
This is what they call a compound mosasaur jaw. The teeth are real, and parts of the jaw are, but they come from different mosasaurs. Some of the jawbone is from modern animal bone, other parts real fossil bone, sometimes plaster.
The matrix is made of crushed origional rock, which is then mixed together to form the matrix which the jaws are set into.