sourceless quick google

It could be including childcare, increased housing costs for larger housing, any myriad of things.

https://smartasset.com/financial-advisor/cost-raise-child-2023#:~:text=The%20ongoing%20costs%20of%20child,the%20U.S.%20is%20%2420%2C813%20annually.

This was the article at the top of google. Looks like yeah childcare + housing are the majority of the costs.