what is.......

dress up the baby

incorrect

dress up it means wear clothes............

If you're able to understand Chinese:

dress 穿著/衣著 - to wear or to cloth someone
dress up 扮靚/盛裝 - to formally dress and make up to the best outfit for a event.

Hope this tell you the differnce and you'll be able to write/correct.

Don't try to be English when you're clear don't "fun"中英文字in the same sentence.