As someone who is on warfarin, I have the same impresson of an INR of 4.8 as you do -- that it is undesirable but not greatly alarming. I have never heard that the INR is interpreted any differently for an infant than for an older person. There are some "heart mom" forums on the internet for mothers of children with congenital heart disease. I don't know where to direct you, but if you can find a forum such as that, this is a question that some of the other moms might know. Also, obviously, it is something you can ask your son's doctor. But as an adult on warfarin, I have never heard that a child or infant's INR means anything different than an adult's INR.
Hello and hope you are doing well.
It is usually recommended to have an INR of 2.0 to 3.0 for basic "blood-thinning" needs. If the INR is higher - about 2.5 to 3.5, it means it is more thinner to prevent clotting. If lower it is thicker. So, if the INR is at 4.8, the chances of bleeding are more, keep monitoring and try to bring it under the normal range.
Hope this helped and do keep us posted.