"I'm going to wait a while, definitely," she tells PEOPLE. "I'm not going to rush into having another kid."
Bristol, 19, who reconciled with former boyfriend Levi Johnston, 20, says their 18-month-old son Tripp "will have a brother or sister, eventually."
Having earlier said she hopes the three of them will now "be a family," Bristol also hints the couple could have an even bigger household, given that she enjoys being around a lot of kids.
"I miss my home because I've got my little brother running around there. I've got all my little sisters, and I just miss that," she says.
"And that's why Willow and Piper and Track are always out here," she adds. "I just miss that environment."
Reporting by SANDRA SOBIERAJ WESTFALL