Your dreams are all about you and what you need, not about "reality" so whatever your son at an early age "means" to you, and it doesn't have to be about your son at all, is why he is that age.

In other words, your dreams with your young son in them could be about something else that happened during that period, about the number four (a shortcut for your head, in my case, I might see clover as I use to collect 4-leaved clover or I might see my grandmother and clover as she taught me and she and I use to look for 4 leaf clover together, etc.) or it could be about your son at that age or another child at that age, etc.

Did anything happen 12 years ago (or 4 years ago)? Is "4" a significant number to you? (It's my lucky number) or are there two children in your family, and yourself and husband or did you have one sibling you feel got more/less attention from your parents, etc. Did anything happen in the day before the dream that might have triggered a dream about your son, at all? Maybe you really enjoyed your son at that age or had trouble with him then or he's having trouble now and you unconsciously think it started then, etc.

Maybe, since he's not necessarily "4" but just somewhere under that age, your dreams have to do with when you were in high school or college, 4-year institutions. He's in high school now, would make sense to me to have a dream about him at age 2, 3, 4, to get your attention in thinking about something that is related to your high school years? Maybe you did something well/ill then and are afraid for your son to do the same or he's having a problem now that you don't think you understand but if you'd remember your own time at that age, might, etc.