I have three children, ages 5, 8, and 11. I have never counted presents, that is just ridiculous in my mind and teaches greed and me me me! I spend approximately the same amount on each child, but God help them if they ask for an accounting record or start counting gifts and complaining... I put out the gifts I've already wrapped several days ago, and of course they checked them out when they got home :) they def noticed how many they each had, and I overheard them talking about how some must be more/less pricey than the others gifts and maybe I've still got more to wrap. My older kids told the little one that she sure has a lot to open, but not in a mean way, just in a noticing way... I want my kids to grow up learning that fair is fair, but not always equal. They know I spend about the same amount of money, it's never been an issue. The little ones have a combo gift from one set of grandparents, so one gift for the two of them. The older has three less pricey gifts from same set of grandparents. Now, in your exact situation, your kids are young... So if you're talking one gift versus 38 gifts, that's not cool... If it's 15 versus 20, I wouldn't worry about it! Oh, and to the folks saying 5, 7, 9 year old kids can't understand money,yes, yes they can!
ETA: also, all three of mine have bdays right after, one is 12/26, I would never give him less just bc he's getting bday presents the next day. They are two totally separate things with two totally separate budgets.