What child's size is the equivalent of a women's size 4 in clothing?

It's really touch and go, because the shape of a child's or teen's body is different from a woman's body. The closest size to a women's size 4 is a child/tween size 16.

[Women's] size 4 - Bust - 34 | Waist - 25.5 | Hip 36.5

[Girls ages 7-14] size 16 - Bust - 33.5 | Waist - 27.5 | Hip 36.5

Going up to a plus size child or tween size and making some alterations would probably be the safest route to take if there is something you really like in the teens section that you can't find in the adult section. Been there myself, something really cute in the tween or teen section that you just can't pass up.

Also when in doubt.. try it on.. that's what I do!