C.M.
Hi M.,
I am a mother of two boys who are 22 months and 3 months. My underarms did not darken with my first son but they did with my second. They got lighter gradually and are now back to normal. I would say it took about two months for them to return to its normal color. How old is your youngest child? Did you just have a baby and your underarms have darken since or have your underarms been dark since your oldest child who is now 8? If you have just had a baby then I would not worry. They will eventually lighten. Good luck!