Hello. I am very sorry that your grandson is so sick. Unfortunately, we have a lot of experience with RSV and other respiratory ailments. Our 5 year old has been admitted to the hospital 4 times for 4 days each from age 2 thru 4 with respiratory problems. This is so scary, so stressful. Her oxygen levels dropped so low that she was hospitalized until they reached a normal levels again.
First, most children really do rebound from this well. It is, again, very scary and so sad to see your child suffer, but after few days of treatment, kids seem to rebound quite well. We have a nebulizer and steroid treatment at home just in case we ever need it.
I, too, breastfed our children. Really, this has nothing to do with your grandson getting sick. Your daughter should be proud of herself!
As your grandson grows have his adeniods and tonsils checked. This will not prevent further respiratory problems, however we discovered that our daughter's airway way 80% blocked by incredibly large tonsils which we had removed at 4 years of age. She still gets colds, runny nose, etc...however she has not had an respiratory issues to speak of. I am still gun shy, so when she has a cold I do give her nebulizer treatments (under Dr's care) when I think she is a bit uncomfortable in her breathing.
AND call your Dr. if you feel your grandson is getting worse, not better. Trust your instincts.
Sorry this is so long! Please let me know if you have questions. Good Luck and I hope your grandson is already feeling better!!