I assume the turkey crown will have the appropriate time and temperature on the packaging? Or that your son (even if he is not a very good cook) is capable of reading a cookbook or looking up the internet? There is plenty of advice out there on thoroughly cooking poultry, as well as plenty of scaremongering about Christmas food poisoning.
There is nothing intrinsically different about a larger pice of meat than usual. Most of the problems occur because people either don't know the rules or can't be bothered to follow them.
1) Store it safely at below 5 degrees C. If it is frozen, defrost it thoroughly before cooking.
2) Wash hands before and after handling it.
3) Preheat oven to the right temperature.
4) Cook it for the recommended time.
5) Test it either with a food thermometer (at least 75 degrees C in the centre) or by piercing it to the centre with a skewer or sharp knofe and checking that the juices run clear.
6 ) Let it rest for a short while before carving it to allow the temperature to even out all through it.
7) Cover what is not carved for immediate use, while you eat.
8) Carve the rest as soon as you can and pack the slices in single portions to freeze and eat later.
Even better, get in plenty of rolls, butter them and fill them with sliced turkey, and freeze those - taken out of the freezer first thing in the morning, they will give you an instant light lunch on several grey days in January and February.