The So Macho singer has said that Simon often jokes around with her own children, Magdalena, eight, and Zac, six, and they have taken to calling him "Silly Simon".
"Simon does everything naughty," Sinitta was quoted as saying in The Sun. "He shows them food in his mouth when he's eating and gives them loud toys to bang in the bedroom when I'm trying to sleep. He's great with kids. He becomes a third child."
The Britain's Got Talent judge is expecting his first child with US socialite Laura Silverman, and has kept a low-profile since the paternity scandal broke out last month.
Sinitta is not the first person, however, to reveal that Simon would make a good father. Fellow talent show judge Amanda Holden has previously said that Simon has a natural affinity with children, especially younger ones.
"He asks children brilliant questions – he'll say 'Right, which one of you is the naughtiest? – and they're all so doting on him," Amanda once told HELLO!
"I want him to have children because he would genuinely be a fantastic dad because he is good fun," she told The Sun. "But there is no way he would go near a nappy or a poo or anything like that."
"When the baby's walking and could have a conversation with him and know who he is, that would be fine."
Simon's mother Julie was extremely excited to hear the news, saying, "It's wonderful. He'll make a fantastic father."