What would you do if this was you?

I have a problem with fairness in my Family. Every Christmas & on their Birthdays I buy my Nephews & Niece expensive presents & always acknowledge them but when it comes to my kids they get ignored on their birthday's & for Christmas they are lucky to get $5 each spent on them I know it's the thought that counts but my kids are noticing that I spend approx $400 total on 4 kids in a year Christmas, Birthday & Easter and they are now resenting how they're treated in comparison to their cousins. Is what's good for the goose good for the gander?