Rob Kardashian kicked off his birthday celebrations with girlfriend Blac Chyna on Wednesday.

The reality star enjoyed some pre-birthday fun with the 27-year-old model and her 3-year-old son, King Cairo Stevenson, at Legoland theme park in San Diego, Calif.

Kardashian and Blac Chyna were all smiles as they took King around to the various attractions. The reality star, who turns 29 on Thursday, March 17, showed off his slimmed-down physique next to Blac Chyna in photos.

"Pre Birthday Turn Up," he captioned a picture of himself with the model.

Sources told Us Weekly the pair "both looked so happy" when they stopped for gas on their way to San Diego. The couple enjoyed a dinner out together that night, and Kardashian received plenty of love from his family the next day.

"Happy birthday Rob! God blessed me beyond measure the day you were born," mom Kris Jenner said on Instagram. "You are the most amazing man who is kind, funny, smart and you have the best heart."

"You are beautiful inside and out and have brought so much joy to my life," she added. "Thank you for being the best son a Mom could ever dream of... I love you sooo much @robkardashian and I'm so proud of you. #blessed #love #happybirthdayrob."

"Happy birthday to my sweet brother! My best friend! My ace forever!" sister Khloe Kardashian wrote on her website.

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"My love for you knows no bounds. You are and will always be my ultimate and all I ever wish for you on this day and everyday is your true and complete happiness. I love and adore you Rob!! No one will ever get our bond and I love that!"

Kardashian and Blac Chyna have been linked since January and are genuinely in love, according to Blac Chyna's best friend, Amber Rose.

Blac Chyna shares King with her ex-fiance, Tyga, who is dating Kardashian's half-sister, Kylie Jenner.