Heidi Klum Martin Kristen Lou Henry Johan

Heidi Klum Martin Kristen Lou Henry Johan

It's hard to believe that ageless beauty Heidi Klum is actually 40 years old.

The model celebrated her big 4-0 on Saturday with a hat-themed party in Culver City. Heidi's bodyguard-turned-beau Martin Kristen and her children Lou, Henry, and Johan attended the party, which was thrown by one of Heidi's friends. Real Housewives of Beverly Hills star Yolanda Foster was also in attendance.

Her adorable children dressed according to the theme, donning derby and Panama hats for the occasion. Lou was the only one who chose not to sport a lid, instead letting her wild mane flow free.

Klum took to Twitter earlier that day to show her children's thoughtful gift: painted molds of their tiny hands.

She also posted a photo of her party, where she wore a gigantic three-piece top hat. Check it out after the jump.