Charlie Sheen's Jumps on Nanny Train with New Girlfriend

Charlie Sheen's joined the craze that's sweeping Hollywood ... nannies can be super fun to date.

Charlie's followed in the footsteps of Jude Law, Ben Affleck and Stephen Belafonte ... except he's not married.

Charlie's boo is 26-year-old Julia Stambler, a model who used to be the nanny to his 8-year-old twin boys. Charlie's ex-wife, Brooke Mueller, hired Julia around the time Charlie was engaged to Brett Rossi.

And get this ... Brooke's the one who introduced Julia to Charlie!!!

Julia's been modeling for 3 years ... lots of bikini modeling. She was also an extra on "Entourage."

She's actually been dating Charlie for 3 months, but they kept it under the radar until this week.