Caskett is married with kids when 1x01 happens and no one knows because they keep their personal and professional lives separate. The boys and Lanie find out during 1x01
I don't know if they could get away with nobody knowing, especially considering that Lanie and the boys are Kate's friends as well as coworkers. They would most definitely notice little Caskett's running around and Kate would have at least one photo of her family on her desk.
But I like the thought of them being married during 1x01 so I'll roll with that.
He hated book launches, especially when his wife and children couldn't be there. Kate had to work and Alexis had stayed home to babysit her three younger siblings, RJ, Joey, and Marti, leaving just Castle and his mother and a swarm of giggling bimbos vying for his attention.
He's already been asked to sign about a hundred chests and it's not even nine yet. It's going to be a long night, especially when people learn of his plans to kill off Derrick Storm (Kate had nearly clobbered him).
"Oh, don't look so blue, kiddo," his mother said, stepping up next to him at the bar. "You'll see them all at the end of the night."
"Only if Kate's case is closed and the kids are still up, which is unlikely. Alexis has a magic that neither Kate nor I have learned yet."
"It's called warm milk," Martha replied. "Knocks them right out."
"What I wouldn't give to be knocked out right now."
"That can be arranged," a voice said from behind him. Castle turned to see his wife standing there, in the suit she'd been wearing when he dropped her off at the Precinct earlier, before his party. Her work suit.
"Kate?" he gasped, a smile spreading over his features. "What are you doing here? I thought you had a case."
"I do," Kate replied, holding up her badge. "It's why I'm here."
It was past midnight when they returned home to the quiet of the loft. Alexis was still up, sitting at the kitchen island with her book open in front of her. Kate walked up behind her and peered over her shoulder.
"Whatcha readin'?" she asked, startling the redhead, who turned on the spot with a gasp and glared at her stepmother, who snorted as she got whacked.
"You wanna give me a heart attack?" Alexis admonished. Kate honked out a laugh and hugged the girl tightly. It took only a couple of seconds for Alexis to stop resisting and sink into her embrace.
"How goes the studying, Nerd?" she asked, keeping her arm over Alexis's shoulder as she looked down at the Chemistry book.
"It goes," Alexis replied with a sigh. "How did it feel arresting dad?"
"Like the first time we met; thank God he was wearing clothes this time, though." Alexis wrinkled her nose.
"She didn't arrest me," Castle interrupted, coming out of his bedroom, where he'd deposited his coat and tie. "Just brought me in for questioning...and let the boys rough me up a little bit."
"I'm sure they enjoyed that," Alexis snorted.
:"Oh, they did," Kate confirmed, walking to the fridge and pulling out a can of whipped cream, spraying it into her mouth.
"Ooh, did they make you their bitch?" the girl asked her father.
"No, I'm afraid that claim still belongs to you, Switchblade," Castle quipped, kissing her forehead and snatching the can away from his wife, spraying some in his own mouth, before offering it to Alexis, who shook her head.
"Already brushed," she said.
"Suit yourself," Castle replied, spraying some more, before offering the can to his wife. "Baby bird?" he asked. She nodded and he sprayed some in her mouth while Alexis looked on, shaking her head.
"You know," she said, "sometimes I wonder who's really the adult here."
Kate snickered at that and shook her head, kissing Alexis's forehead. "Go to bed, old woman," she said. "You've got a test tomorrow. Did the monsters go down easily."
"Yup, all it took was a little whiskey and--"
"Alexis!" they exclaimed in unison.
"Kidding, obviously," Alexis replied, rolling her eyes. "Yeah, they went down just fine. Marti's got a little diaper rash though."
Kate frowned at that. "Maybe I should go check on her," she said, making her way towards the stairs. Castle pulled her back.
"Let them sleep," he said. "They'll call us if they're in distress; meanwhile, we've got some research to do."
"Research?" Alexis asked, packing up her books to head upstairs. Castle nodded.
"Some guy is killing people based off of my books." Alexis's eyes widened.
"Oh, I'm so sorry," she said.
Castle shrugged. "It's not my fault," he said. "But if I can help find whose fault it is, then I'll feel a lot better about it."
"I hope you do," Alexis said, standing up. Castle smiled and wrapped his arms around her, kissing his daughter's forehead.
"Thanks, Pumpkin," he said, before pushing her in the direction of the stairs. "Now go to bed."
"Goodnight, guys," she called out over her shoulder as she sprinted up the steps.
"Good kid," Kate murmured.
"Fantastic kid," Castle concurred.
"Let's hope the others take after her," she said, "instead of me."