This is what my baby care book by the American Academy of Pediatrics have to say on lead poisoning.
"During the first two or three years of life, your child is bound to go through a phase of putting things other than food into his mouth. He'll chew on his toys, taste the sand in the playgound, and sample the cat's food if given the opportunity. As annoying as this can be for you, few of these things will cause him any serious harm, as long as you keep poisons and sharp objects out of his reach. Lead is one dangerous substance, however, that your child can consume without your knowledge."
"Contrary to popular belief, lead poisoning is not caused by chewing on a pencil or being stabbed with its point. The so-called "lead" in a pencil actually is harmless graphite, and there is no lead in the paint coating the outside. Lead poisoning is most often caused by eating lead contained in bits of old paint or in dirt that has been contaminated by lead, by breathing lead in the air, or by drinking water from pipes lined or soldered with lead."
I believe your baby should be ok. Trust me, my 3 babies have put worse things in their mouths than erasers and pencils....