I didn't know anyone could have "little bit of MRSA"...you either do or you don't.
MRSA is Methicillin-resistant Staphylococcus aureus (MRSA) and known to most as multidrug-resistant Staphylococcus aureus ...which means it is resistant to most if not all antibiotics.
First and foremost DO NOT PANIC. Get educated by your doctor and hospital - if you google it - you might just freak yourself out - as you are not a doctor and might read the stuff and just freak.
Since your son already has a depressed immune system from multiple surgeries, the place to pick up MRSA is the hospital....so talk with the hospital and pediatrician about what they told you and what they are going to do.
I don't know if you can be a MRSA carrier and never have it...kind of like other diseases - people are carriers and never had the disease.
Good luck - I hope your son is fine and it's NOT MRSA!!