Simpson was blasted online after the pics of Maxwell getting her long blonde hair layered with purple, pink and blue rainbow pattern inspired by Disney's "Descendants" were posted earlier this week, with some people commenting about how it was "so sad" and suggestions that it was shame she was "ruining her hair so young."
Pink, who has had several run-ins with "mummy-shamers" later jumped to Simpson's defence and posted pictures of her daughter Willow, eight, getting a home dye job.
"I heard people were bummed on Jessica Simpson for letting her seven year old get her hair colored," she wrote on Instagram on the post. "So we thought we'd share what we did yesterday. #bluehairdontcare #getyourownkids #parentpoliceareactuallyjustlonelysadpeople #illdyeyourhairtoolosers #ohlookmanocomments."
While she has disabled comments underneath the image, more than 750,000 people have liked the snap so far.
It's not the first time that Pink and husband Carey Hart have let Willow rock some colour in her locks. Last year dad Hart shared a photo of his daughter with purple hair.