The elephant in the room? Tristan Thompson's third child is growing up fast.

Theo, 19 months, was seen in new pictures enjoying a day at the San Diego Zoo with mom Maralee Nichols. On July 14, the influencer shared photos of their visit, including sweet pics of them checking out an elephant enclosure. "Adventures with Theo," she wrote on  Instagram. "No place I'd rather be."

In the pics, the little boy wore a white T-shirt, blue denim shorts, a blue bucket hat and Nike sneakers to their outing.

The zoo was not the only spot the mother-son duo visited recently. Maralee also posted a photo of herself pushing Theo on a swing in a playground near a beach. 

She gave birth to the boy in December 2021, months after filing a paternity suit against Tristan, which revealed the news that he had fathered a child while dating Khloe. In January 2022, after it was established that the basketball star is the boy's father, he issued a statement of apology to the Kardashians star.

The following July, Khloe and Tristan welcomed their second baby together, son Tatum Thompson, via surrogate. The boy joined the now-exes' eldest child, daughter True Thompson, 5.

Tatum is Tristan's fourth child overall—the athlete also shares son Prince Thompson, 6, with ex Jordan Craig. The NBA player has occasionally shared photos of his eldest kid with True, while Khloe often shares pics of both their kids.

See Maralee's cutest photos of her and Tristan's son Theo below:

On July 14, 2023, Maralee shared this photo from her and Theo's trip to the San Diego Zoo.

Theo meets an elephant.

Maralee pushes her son on a swing.

Theo checks out his surroundings on a day out with mom.

This boy holds the key to his mama's heart.

Maralee Nichols documents her son Theo Thompson enjoying a Southern California sunset. 

While exploring an aquarium, Maralee revealed Theo's "favorite words are 'wooow' and 'coool.'" 

It's a magical mother-son date at the Disneyland Resort in Anaheim, Calif. 

Maralee celebrates her first Halloween as a mom alongside baby Theo. 

"October with my pumpkin," Maralee shared on Instagram. 

You never know who you will find at the pumpkin patch! 

"Can't believe my baby is 6 months old," Maralee wrote from the San Diego Zoo in June 2022. "Theo's first time at the zoo, he loved looking at all the animals."