If a child eats too much metal (coins) can this cause them to have learning disabilities?

I doubt it: After decades of practice and additional training in learning disabilities, I have never heard of coin ingestion influencing ld. Most pass thru the body in 3-5 days and the metal involved is not considered toxic. There might be issues with a kid gnawing on lead toys but not coins.

Why are they eating : Coins? This should be checked out and stopped in an appropriate way. It sounds like pica, but still why is the child eating coins at all. See a psychologist and a pediatrician.

PICA: Your child has PICA, eating of non food substances. The metal in the coins is not likely to cause learning problems, but are lead paint chips or is the child chewing on painted surfaces. If so, then you should have a test for blood lead level and speak to your pediatrician about the PICA.