It depends on the allergy pill and the child. Symptoms of an overdose can range from feeling restless or nervous, nausea, vomiting, stomach pain, dizziness, drowsiness,to a seizure. So i would get in contact with a doctor asap.
411 your local poison controle center for next time, and trust me their will be a next time. the child will probly be find just very sleepy
Depends on the med... but most likely nothing, what is more interesting is why this child was allowed (or wanted) to take the meds...
I think the child should be ok, but it wouldn't do any harm to contact poison control or a doctor.