So apparently 3M puts out an interesting and free First Aid manual. Those of us who are professionally trained might get along without it just fine, but I ordered it for information such as this (because when the day arrives and I have a child with a fever you just know I am gonna be freakin'):

call doc if baby under 3 months has rectal temp of 100.5 F or more, 102 F for baby older than 3 months