Britney Spears is hoping to regain custody of her two toddler sons by painting her former husband, the boy’s legal guardian, as a weed head.

A spy tells Life & Style: “Britney believes Kevin’s been smoking pot in front of the kids. She says she can smell it in the boys’ hair and on their clothes when she has her visitation with them.”

“She’s asked the court-appointed monitor and her lawyers if they can prove the kids have been exposed to environments in which drugs have been taken.”

A friend of Kevin’s insists Spears’ ex-husband “never smokes (pot) around the kids.”