The star is engaged to PR boss Simon Motson and has two children – Ava and Hero – from her relationship with ex-husband Graham Quinn.
She welcomed her 20-month-old son Apollo with Simon in August 2019.
The singer, 43, said being in that type of family and being a step-parent meant you had to be “the most mature you can possibly be.”
Discussing the challenges on the Made By Mammas podcast, she explained: “It really takes you being the most mature you can possibly be, even when you don’t want to be.
“I said to Sim when we were first all living in the house together, I said that I’m not going to tell your children off because I don’t feel like that’s my role.
“And within 10 minutes, that’d gone out of the window when one of them is hanging off the monkey bars and another is trying to put a ball through a window.”
She continued: “In the end, I just changed all that around and I sat them down around the table and said look, the only way we’re going to do this is, I see it as we’re all in a boat, this is how I view it.
“And one of you rocks the boat, we’re all going to feel it. And if one of you goes overboard, I’m going to grab you and make sure you’re safe. That’s the only way we’re going to get through it, is if we’re all in this together.”
Simon and Myleene dated for five years before he popped the question towards the end of last year.
He initially proposed with a gold promise ring with a shiny diamond in the centre.
The ring was a place holder until she finished designing her ultimate dream rock – which turned out to be a super-rare black diamond.
She showed off the design on Instagram last year as well as the process, which was all thanks to jewellery designer Ira Kormind.
The Hear’Say singer explained: “After Sim proposed I got it into my head that I wanted a coloured diamond for my ring. I had no idea where to source a rare, black diamond.”
She added: “I love everything it stands for, what it means for us to have made it together, what it took to get here in the first place and ultimately, because it’s unique, super rare and was made with friendship and love.”