Contemplating a 4th child, what are the financial implications?

Thinking of Going from 3 children to 4.
Currently children are 7, 4 & 1.
Would love a big family.
For those with families of 4, what do you find the hardest? What is the financial implications from 3 to 4? I found it more challenging physically going from 1-2 children. But want to hear from others their experiences financially with 4.
Thanks ladies!