At what temperature should i take my 2 year old to the doctor?

100.4: Most doctors would probably say at 100.4, but it will depend on other symptoms: whether he/she eats well, appears healthy otherwise, if has a cough, diarrhea, ear ache and many other factors.

105f or 40c: These numbers are only guidelines.Remeber the overall picture.Is there difficulty breathing, dehydration, severe pain, lethargy, disorientation etc, all of which may occur with lower or even no fever.

100.5: 100.5 is considered a fever. With any fever it doesn't hurt to have a 2yo checked out by a doctor. Even without a fever if their symptoms are severe get them checked. Keep in mind that a fever and a trip to the doctor doesn't necessarily mean you'll get an antibiotic. Most infections are viral and don't need an antibiotic. Trust your doctors recommendation. Sometimes tincture of time is the best.