The online retailer will also assume $45 million in debt from Quidsi, according to a statement from Amazon.
"This acquisition brings together two companies who are committed to providing great prices and fast delivery to parents, making one of the chores of being a parent a little easier and less expensive," said Jeff Bezos, founder and CEO of Amazon, in a statement.
The management team at Quidsi will continue to run the sites and operate them independently, Amazon said.
The deal has already been approved by Quidsi shareholders. It is expected to be finalized in December.
Amazon will also take ownership of BeautyBar.com, a new site recently launched by Quidsi as a beauty boutique.