2 year old taking 1 advil, what side affects will happen etc?

Children can take ibuprofen (Advil)... did the child take a 200mg tablet? What is the weight of the child? Maximum doses given for fevers is 10mg/kg orally every 6 to 8 hours.

So if the child is less than 20kg (which would most likely be the case) then this is quite a high dose and they may experience side effects. The recommended maximum daily dose is 40 mg/kg (given in 3 divided doses).

Seek emergency medical attention if too much of this medicine is taken. Overdose symptoms may include nausea, vomiting, stomach pain, drowsiness, black or bloody stools, coughing up blood, shallow breathing, fainting, or coma.

https://www.drugs.com/ibuprofen.html

https://www.drugs.com/dosage/ibuprofen.html