Parents: Your messages to your children about clothes, sexiness, etc, needs to be consistent across their childhoods. There’s not one (more permissive) message that’s right for babies and another (less permissive) message that’s right for preteens and teenagers.
I took this picture at the local Walgreens this morning. I’m going to give all of you Parents and Parents-To-Be a rule of thumb about your children’s clothing:

If you would be upset at your daughter for dressing a certain way at 13 or 16 or 19, you should never dress her that way.

This applies to words as well. If you would be concerned by your daughter asking you if her jeans make her butt look big at 9, you shouldn’t put her in a baby tank that says this.
Yes, I get it, it’s ironic. Diapers DO make babies’ butts look big. And this is a stereotypical question that women ask about jeans. So making it be about babies is somehow ironically cute.
But no, it’s just tacky, it’s just teaching your child to examine and critique their body and their clothes for what might make them more sexually appealing. It’s also teaching other people to examine and critique your child’s body and clothes for sexual appeal. Is that really what you want?
Never mind that lots of people love a woman with a large butt. Never mind that when you have a biological condition (like the need for diapers), being concerned that it will make you less sexually desirable is a screwed up way to face the world. Never mind that even considering whether babies are sexually desirable is very screwed up.
This sort of thing makes me SO angry.
I wish this were a one-time circumstance. But it’s not. It’s really, really not.
SO WHAT’S THE DEAL?
Why do people keep making this sort of thing? It’s only because people are buying them.
So why are people buying them for their own/other people’s children?
I don’t have an answer to that question. But I do know that now it’s time to stop.
These kinds of clothing make us believe that children should strive towards sexiness because it’s cute. Until, that is, they are suddenly 12 or 13 and Daddy’s getting his shotgun because now the children are actually considered sexy, and the children are suddenly told they really need to start buttoning it up.
Stop the insanity, people! Dress your children like children! When they’re babies and toddlers and children you have all of the control. If someone gives your child something that’s inappropriate, either give it back, return it to the store, or throw it away, depending on the circumstances.

You are not powerless under the crush of society.

So take control, consider the long-term educational impact of the decisions you’re making, and be clear about your morals and values. Let your baby know that you love her because of who she is, not because of anything about her physical appearance. (That I just typed those words makes me so very, very sad.)
If you remain unclear about exactly how to go about this, here’s a wikiHow tutorial called How to Buy Appropriate Baby Clothes. Because apparently this needs to exist and be more widely advertised.