Gwen Stefani thought she could ''be really free'' with her kids.

The 'What You Waiting For' hitmaker didn't think she'd have to worry about being strict with her children - Kingston, 11, Zuma, eight, and Apollo, three - because she had been ''free her whole life'' but later learned they felt ''safest'' when there was some sort of boundaries.

She said: ''I was in a band and free my whole life, so I always thought I would be really free with [my kids] and do whatever I wanted, like, 'Oh, I'll take them out of school.' But you learn that when they have boundaries is when they feel the safest.

''The hardest thing to do is having a discipline chart and follow up on all those things. It's work, you know? But that's where you get the results.''

And Gwen - who has her three children with her ex-husband Gavin Rossdale - worries her kids will grow up being ''naughty''.

She added to People magazine: ''I see a constant fear of 'How am I gonna make sure these kids are good people?' I feel like naturally it's so easy for them to be naughty, and you get more and more worried about it the older they get ...

''What I learned about having kids and having a career is [it's] not all about us. You realise that they only want you to care about them. It's just that automatic, like, 'You're my mom!'''

Meanwhile, Gwen's kids joined her on tour in the past and had ''the best time''.

She said previously: ''They had the best time. Can you imagine three little boys on a [tour] bus after you do a show like, 'Get to bed!' ... It's exhausting. But it was fun.

''Zuma was so into it ... I have a quick change where I was changing costumes and stuff - he was working it. He had his flashlight, headphones; he walked me on and off the stage every single night. For two hours he worked back there - he was so into it.''