They say kids change everything – for these celebrity moms, that certainly seems true! These celebs have discovered that a tiny human being can have the biggest impact on their lives.

As a result, they’ve all but given up the identities that made them famous in favor of a more “mommy” persona. Check out these before and after photos of some of our favorite transformations:

Jessica Simpson

Jessica has officially stepped out of her daisy dukes and cowboy boots and into motherhood! For most of her teens and twenties, the public saw her as a fresh-faced pop star or the bubbly blonde star of the reality show “The Newlyweds.” But the lady who had a reputation as somewhat of a ditz – remember the infamous “Chicken of the sea” misunderstanding? – is all grown up and has shown that she’s got a good head on her shoulders.

The mom of little Maxwell Drew is expecting her second child with fiance Eric Johnson. She heads up successful beauty, hair product and shoe lines and has even been a mentor in NBC’s new reality show Fashion Star with Elle McPherson.

Nicole Richie

Nicole has transformed from your typical Hollywood wild child to a rather classy mom. While Richie was once known for her battles with heroin addiction, her stint on the reality show “The Simple Life,” and generally appearing way too thin, she has embraced motherhood and really turned things around.

Now she’s a poised and polished mother of two who founded her own fashion line. She and husband Joel Madden have also worked with UNICEF to create The Richie Madden Children’s Foundation, which provides aid and opportunities to children both within the United States and abroad.

Britney Spears

It’s hard to decide if we want to remember the “old Britney” as the innocent teenager who sang “Oops I Did it Again,” or the sexy vixen who came up with “Toxic.” Either way, it’s pretty impossible to forget the unfortunate head-shaving incident (and mental breakdown) of 2007, but at least Britney has shown us that she can learn from her mistakes.

The past few years have treated her well, and it seems that Britney has learned a lot about growing up from caring for her sons Sean and Jayden. She’s looking better than ever fresh off a stint as a judge for the of “The X Factor,” and who knows what the future will hold?

Jenny McCarthy

This Playboy model and former host of MTV’s Singled Out has had quite the colorful (and nude) past. But while she’s bared it all several times (her latest Playboy cover is her sixth!), she’s also helped parents everywhere by opening up about her personal life – specifically raising a child with autism.

McCarthy has written several books on the challenges she’s faced with her son Evan, and she’s become an active advocate for children with autism.

Snooki

It looks like having a “little meatball” changed this Jersey shore party girl for the better. Nicole “Snooki” Polizzi has traded in the alcohol and fake-bake tan look for an engagement ring from fiance Jionni and a self-proclaimed new chapter of her life.

During her pregnancy, she moved out of the party scene at the Jersey Shore house into her own pad. And since giving birth to son Lorenzo in August, she’s been looking great!