The singer spent a few hours on both Monday and Tuesday with Jayden and Sean ... according to our sources. No word on how their gift exchange went down, but can't imagine the boys left empty-handed. For her part, we're told Brit was thrilled to have the time with them.

We're told Jayden and Sean returned back to their dad Kevin Federline's home afterward -- and they'll be with him for Christmas Eve and Christmas Day. Last year, it was Britney's turn to have the kiddos to herself on the 24th.

Of course, Kevin has primary custody of both children ... Britney cares for them about 30 percent of the time -- something that's been in place for a while now. While many wondered if her #FreeBritney saga would affect visitation ... we've learned it hasn't, and the boys are seeing their mom as regularly as they always have.

In the meantime ... Britney and her dad, Jamie, are still locked in a court battle over her conservatorship. She's made it clear she wants him to step down and hand over the reins.