Sandra Bullock is playing full-time mother to her five-year-old stepdaughter Sunny, because her husband Jesse James’ ex-wife is behind bars.

Porn star Janine Lindemulder, Sunny’s birth mother, has been sentenced to serve six months in federal prison after she was found guilty of failing to pay more than $200,000 in income tax.

And, when she is released, she must spend a further spell living in a residential community corrections center.

Celebrity mechanic James has been handed full custody of Sunny while Lindemulder is in prison, and could appeal to become her permanent full-time carer.

Sources tell the National Enquirer Bullock is desperate to be a mom, and she’s thrilled to get the chance to try motherhood with Sunny, who was born after James and Lindemulder split, and he began dating the actress.

The insider says, “This is a dream come true for Sandra, but it’s Janine’s worst nightmare. Janine is worried that, while she’s in prison, Jesse will file another motion with the court to gain permanent full custody. Sandra loves Sunny like her own flesh and blood, and will completely support Jesse if he chooses to fight for full custody.”