See below. http://www.diffen.com/difference/advil_vs_tylenol both medications used to relieve pain and fever, there are major differences in their mechanism of action and side effects.
Little difference. There is little or no visible difference in a child, between taking acetominophen (brand: tylenol (acetaminophen)) or Ibuprofen (brands: advil, motrin). Both are for treating fever, pain, and inflammation. Always be sure the dose is correct, and do not "double-dose" by giving other cold medicines that also contain tylenol (acetaminophen) or ibuprofen. Tylenol (acetaminophen) can be used for babies over 2 months, & Ibuprofen over 6 months old.
Time + side effects. The biggest different is that Ibuprofen lasts 6-8 hours, while Acetaminophen dosing is every 4 hours. Ibuprofen can upset an empty tummy and -- rarely -- can harm the kidneys or intestines. A large overdose of Acetaminophen can damage the liver. I personally prefer Acetaminophen for the first six months of life.
Anti-inflammatory. Both are pain relievers. However, Ibuprofen is both a pain-reliever and an anti-inflammatory. Anti-inflammatory medications help with such things as swollen joints and pulled muscles in a more effective manner than acetaminophen. Also Ibuprofen is broken-down by the kidneys and Acetaminophen is metabolized by the liver. One may need to be avoided in children with kidney or liver disease.
Length of effect. Both treat fever and pain. Ibuprofen lasts 6-8 hours while Acetaminophen lasts about 4 hours. Sometimes, one seems to work better than the other, either for certain symptoms or for certain children. (for instance, i find Ibuprofen more helpful for sore throats, usually.) pick the one that helps the most for your child, for their symptoms. (the "alternating" idea isn't recommended.).
Ibuprofen/acetaminop. Both reduce fever& pain. Acetaminophen (tylenol/feverall) is easier on the stomach, but lasts only about 4 hours. It's available in rectal suppository (a godsend for the vomiting tot w/ fever). It's very toxic when overdosed, though. Ibuprofen (motrin/advil) also reduces swelling (great for sore throats) & lasts 6-8 hours which improves sleep for everyone ;). Follow the label or ask your doctor.
Medication. Acetaminophen is antipyrtec (fever reducer) and pain reliever, Ibuprofen is antipyretic, pain reducer and anti-inflammatory. Acetaminophen works for 4-6 hours, Ibuprofen for 6-8 hours. Tylenol (acetaminophen) is gentle on an empty stomach. If Ibuprofen is taken for a long time on an empty stomach it may cause stomach mucosal irritation.
Chemical makeup. Both relieve pain and fever, but they are chemically different. Ibuprofen works in an inflammatory pathway of the body which also makes it a good medicine for inflammation, which Acetaminophen is not. Ibuprofen can cause problems with the stomach lining and with the kidneys because of where/how it acts in the body. Acetaminophen can cause a problem with the liver if taken in excess.