Shortly after welcoming Lenny in 2015, the children's entertainer said he was overjoyed to have a "mini me".
"It’s just the most amazing thing. To see his little face for the first time… we were overjoyed," Jimmy told Woman's Day.
The 34-year-old said nothing could have prepared him for fatherhood, which has been his favourite role to date.
"It’s so much fun, but also frustrating at times when you don’t know what you’re doing," the doting dad said.
Despite filming taking up three days a week of Jimmy's time, when he's at home he's a hands-on dad with his three children, saying their view of the world is "sweet and naive".
"You forget about everything for a while when you go and do something with someone who hasn’t seen it before. It takes you back to when you were a kid and the joys of life you forget," he told Stellar Magazine.
"When he was younger he didn’t realise. Then he recognised me and would say: ‘Dad, Dad, Dad'," Jimmy told New Idea.
"It took him a while to learn that when I go to work I’m Jimmy Giggle and when I’m home I’m Dad. Now he knows he’s being funny when he says: ‘Jimmy Giggle, do you want to come and jump on the trampoline with me?’
"He likes to pretend he’s a dog. He gets down on all fours and says: ‘Call me little Pongo'."
Just a year into dating, Jimmy and Tori packed up their lives in Victoria and moved to Sydney when Jimmy landed the role on Giggle and Hoot, which he said was a turning point in their relationship.
"It became clear this was a special relationship we were forming,” he told the publication.
“Everything we’ve done has been as a team. It’s a special thing when you find that someone to be your teammate. We just went for it, and nothing’s really been an issue to be honest."
The couple, who have been married since 2013, said their bond as a couple grew even stronger after having kids.
"She’s an amazing woman and an amazing mother," Jimmy told Stellar of the stay-at-home-mum.
"I’ve learnt a lot about being a parent from her. I’m not an A-list celebrity, but when you’re in this little bubble — people telling you that you’re great and that you’re funny — you need someone who can give you a reality check.
"Tori is a total superstar, she was born to be a mummy and continues to surprise me with her innate ability to just know what to do."
The arrival of the twins was all the more special given the struggle Jimmy and Tori experienced with conceiving second time around.
In 2018, the media personality admitted it was "proving a little difficult" to expand their brood.
"We had a struggle falling pregnant. It wasn’t the biggest struggle in the whole wide world, but we had miscarriages and we were so excited, and then we were so disappointed and disheartened," he has previously revealed.
"People don’t talk about miscarriages but it’s just so common. It’s heartbreaking and the same thing going through IVF. It’s demoralising and heart breaking and it’s so hard."
And when he announced Tori's pregnancy on social media, Jimmy captioned the post with a message of support for other couples.
"We started trying a very long time ago and after enduring much heartache, disappointment and feelings of hopelessness we are over the moon," he wrote.
"To all those who are struggling with infertility, miscarriage and the longing to add to your family, stay strong and try not to lose hope."
The couple faced even more struggles when Mack was placed in intensive care at just seven weeks old following complications during a tongue tie procedure.
Mack was rushed to hospital by ambulance before requiring CPR and a blood transfusion.
Thankfully Mack was released from hospital after a couple of weeks, with Jimmy revealing the newborn was "continuing his recovery, still has a very sore mouth but he is getting there."