A former nanny of Britney Spears who worked for the singer eight months ago and witnessed firsthand her controversial parenting skills is set to be a crucial witness in the beleaguered pop star’s bitter child custody battle with ex-husband Kevin Federline, a source tells OK!

Christine Hallet, 37, is one of several individuals, including Britney’s former manager Larry Rudolph, who have been subpoenaed by Team Kevin to give testimony that will decide if he will be successful in gaining majority custody of Sean Preston, 23 months, and Jayden, 11 months.

A source tells OK! that Hallet is expected to reveal the following in her deposition:
•That Britney would often come home from partying in the middle of the night and wake up the babies to play with them, keeping them from gettting the proper amount of sleep.

•That Sean Preston’s teeth were in poor condition and his gums were bleeding because Britney wasn’t brushing his teeth.

•That Sean Preston also suffered from severe constipation because of his poor diet.

•That both boys were getting rashes on their skin because Brit was washing them in bathwater containing designer lotions harmful to a toddler’s delicate skin.

"What the nanny reveals about Britney and how she treats the kids will be extremely important to the case," as source tells OK!

Hallet is one of many close friends, family and employees named in court documents obtained by TMZ.com.

For more on Britney, check out the current issue of OK!, on newsstands now!

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