The 'Biology' singer - who has Bobby, three, and 5-month-old Cole with husband Justin Scott - loves to play music for her boys but her eldest child is unimpressed if he hears her former band.
She told Hello! magazine: ''[Bobby is a typical] threenager. He is constantly testing the water and trying to get a reaction out of me.
''He and Cole love music and the other day a Girls Aloud song came on.
''I said to him, 'Do you like this one Bobby? This was Mummy's band, Girls Aloud'. He went, 'No, I hate Gelz. It's rubbish.' ''
Kimberley was concerned Bobby would dominate over his younger brother because he has a strong personality, but she's pleased that Cole has proven to be a match for him and they are developing a firm friendship.
She said: ''I was a bit concerned that Bobby would rule the roost because he's a big character but Cole gives as good as he gets and, for the most part, they're becoming good mates, which is lovely to see.''
The 36-year-old pop star is finding motherhood ''easier'' now Cole is able to walk and communicate, but she still encounters ''challenges'' when it comes to raising her family.
She said: ''Cole is walking and making himself understood now and I do find it easier, although every stage brings its challenges.''
However, Kimberley insists she isn't ready to have another child.
Asked if it's too soon for baby number three, she said: ''Definitely. I do love babies. But at the moment, we've got our hands full and I feel the balance is good.''
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