2 yr old w/ fever puffy eyes diagnosed w/ mild throat virus... Possibilty of mono. Temp was102.5 mon now is 99.3 wo tylenol (acetaminophen) should I be concern mono?

Viral infection. Your description sounds like a viral infection. If persistent symptoms occur, enlargement of the spleen are noted, or other problem, testing for mono can be performed by your doctor.
Mono in infants. Mono in infancy is usually no more involved than a minor flu. Of course baby can be sickly & have hydration issues but the illness usually resolves within a week or so and confers immunity to the germ. In teens or adults mono can put you in bed for a month & really disrupt your life.