EXCLUSIVE

Honey Boo Boo is already the most famous redneck, and now she's set up to be the richest when she hits 21 ... courtesy of a trust fund set up by Mama June.

June tells TMZ ... the lion's share of earnings from "Here Comes Honey Boo Boo" (a cool $15k - $20k per episode) is being equally divided into funds for all 5 girls ... Alana "HBB" Thomson (7), Lauryn (12), Jessica (15) and Anna (18) and baby Kaitlyn.

June says the little stars can't touch the cash until they turn 21 -- except in case of medical emergencies or using it for school -- saying, "I want my kids to look back and say, 'Mama played it smart. Not like those other reality TV people.'"

In fact, June tells us she never even sees the coin ... "TLC puts the money into the girls' trust accounts for me and then I get an email telling me how much everyone gets."

June added ... "You're never gonna see me drive a Range Rover or a Mercedes. I'll drive one if someone else pays for it. Never gonna live above my means."

As for their means ... Mama June says Sugarbear still rakes in cash from his contractor job, which is how they pay the bills.

The family's only major purchase since suddenly becoming famous is a Ford Expedition ... a 2005.