I know this probably isn't going to be very popular, but you need to consider that kids just don't understand sometimes that not getting them a gift isn't anything personal. My brother and sister in law are financially not as secure as we are, and my mother in law is constantly buying them things and not our children. I love all of them and we all get along fine, but all of us have experienced the grandmother that showered certain grandchildren with gifts and not others, or maybe an aunt or and uncle. When you are a kid, it's hard to understand that. Parents can understand, but it takes pretty profound poverty or extreme wealth for any kid under 10 to understand why it's fair for some cousins to get gifts and not others. Even if their parents try to explain it to them, they just have a hard time getting it. And I don't want to have to put anyone's parents in that situation. I am wondering what I am going to say to my own son when he realizes all of the gifts that his cousins get that he doesn't. It's going to be hard to rationalize when they live in a much larger home than we do, drive nicer cars, etc. Children don't "get" the concept of debt. They are very concrete- what they see is what they understand.
Because of that, I would caution you for sending gifts to some cousins and not others, especially if they live near one another and might find out. Either get everyone a small gift, or no one. A $10 bill or gift certificate can buy a little toy. One year we were tight and I sent cookies to my nieces and nephews. But I sent them all the same thing, so I guess they all could be disappointed together. Who cares about the adults and what they say, but try to remember what it was like to be a child when you were the one who didn't get anything.