A baby's first year goes by fast, as any new mom will tell you — and Carrie Underwood now knows. Her son, Isaiah, just turned a year old on Feb. 27, and the family celebrated little “Fish” with an adorable aquatic birthday cake, of which Underwood posted photos on social media afterward.

The photos show Isaiah’s personal 'smash cake,' reading “Isaiah is O-'Fish'-ally One!” and a matching sheet cake for the rest of the guests, decorated with undersea life and adorable orange fish. The theme is one the family has claimed for the little one, as Underwood’s married name is, of course, Fisher. She and husband Mike Fisher even planned to dress Isaiah as a little fish — with Mom and Dad as fishermen — for Halloween.

Underwood shared her plans for Isaiah's simple birthday party with ET at the Grammys, admitting she wasn’t even sure what she wanted to buy him for a gift.

“[We are throwing] a little party, just family and friends, people that are staples in his life. It won’t be anything fancy,” she dished. “I’m like, ‘What do you get a 1-year-old for a present?’ I have no idea so I’ve been on Amazon trying to find presents for him.”

Underwood is on her sold-out Storyteller Tour right now, but it doesn’t keep her from being present for milestones like these, including Isaiah’s first steps, which he took in Jacksonville, Fla., before her first show of the tour. She’s been lighting up the stage all over the country as she headlines her first road run since Isaiah was born, showing that she’s back and better than ever after taking time off. She’s traveling with Easton Corbin and the Swon Brothers, who joined her recently for a singalong of Nitty Gritty Dirt Band’s “Fishin’ in the Dark.”

Carrie Dishes on Her Babyproofed Tour Bus

See Pics From Carrie Underwood's Storyteller Tour