Yes, as a matter of fact my 3 yr old just got her flu shot in the leg but shes a skinny minnie.

My son missed his booster time at his 18 month so they pushed that shot to his 2 yr, apparently doing it later rather than early is how they prefer it.

Has he been on a regular shot schedule? My daughter had her last set at 18 months. They told me no more shots until 4 years old, except for flu shots.