Maci Bookout's three-year-old son, Bentley, is growing up -- and faster than his mom can handle!

Sending her little boy off to daycare on Tuesday's Teen Mom premiere, Bookout, 20, admits to Us Weekly that giving up 24/7 time with her son (dad is ex Ryan Edwards) was "terrible."

"I wanted him to go so he would have a couple days of the week where he was just playing all day and could meet kids his age," the single Tennessee-based mom explains. "I [set up care so I] could focus on school, but at the same time, I'm used to having him in my pocket all day every day. The first few days were rough on both of us."

Bookout was so distressed over Bentley's latest milestone that she enlisted her then-boyfriend, Kyle King, to take the little guy inside to meet his teacher. (The family's emotional first day apart will be seen on Tuesday's premiere)

As the reality star -- who began her relationship with MTV on 2009's 16 & Pregnant -- prepares to say goodbye to her installment of the franchise, Bookout has plenty of summer plans to keep busy. "He just started riding his bike without training wheels and started T-ball a couple months ago," she says. "I don't want to go anywhere [this summer post-filming] -- I'm actually going to enjoy being at home."

For much more from Bookout -- including how she told Bentley about her split from King, who appears on the latest episodes -- watch the video above now!

Maci Bookout, Amber Portwood, Farrah Abraham and Catelynn Lowell's final season of Teen Mom premieres Tuesday at 10 p.m. (EST) on MTV.