Why do i treat my younger sons better than my older one?

so I have three boys. Tey are 11 and the younger ones are 7 and 2. Well I notice that I treat them better than my oldest son. I treat my baby the best and then my 7 year old a slightly better than the 11 year old. is this normal? Will this effect them in any way? I want to know, because everyone says I ate my oldest son and he doesn't get half the things my younger sons do and I think it's slightly true. Any advice?