Jessica Simpson Shares Adorable Family Photo at Son Ace's 3rd Birthday Party -- See the Pic!

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You only turn three once!

Jessica Simpson's son, Ace, celebrated his third birthday on Thursday and the 35-year-old fashion designer shared a sweet family photo -- with husband Eric Johnson and their daughter, Maxwell -- at his dinosaur-themed bash.

"Happy Birthday dinosaur! You complete me," she adorably captioned the photo.

WATCH: Jessica Simpson's Kids, Maxwell and Ace, Look Almost Identical in Sweet New Pics!

The mother of two was adorably less thrilled to watch Maxwell turn four last month, captioning a pic of her look-alike daughter, "This beauty is at the end of her 3's," and adding the hashtag "HOLDYOURHORSESMAY1"

More recently, Simpson shared a photo of both of her kids together and not only do the little blondies look just like her -- they're practically identical!

The sometimes pop star recently revealed her kids also share her love of music and says they're "already more talented" than she is. Find out if she thinks they'll become singers one day in the video below.