According to Jim (2001) : 1x18

It's Kyle and Andy's birthday, and Andy is feeling a little left out of his own special day. They decide to take him to a restaurant that serves a 4,5 lbs steak, and Jim offers to pay for the check because Cheryl isn't feeling equal to Dana, who's spending a lot of money on their kids. On the table, Dana says she doesn't mind paying the check because she makes more money than Jim, which enfuriates him. He buys a donkey for the girls so they can know he's the one they should go to if they want stuff (in this case, they wanted a poney, but "they'll never know the difference"), and it isn't until the donkey ruins a painting Dana bought for Kyle's room that they talk it out and settle their issues.