The 31-year-old star already has seven-year-old son Bronx with ex-husband Pete Wentz and 10-month-old daughter Jagger with spouse Evan Ross, reported Femalefirst.
"It's a blessing. Kids are the best. I would love to have number three. I'm not ready for that just yet, but I definitely want more.
"Having a child with the person you love is just amazing. She's a little us. Evan is an amazing dad, so it's fun to get to see each other grow in our love and our love for her, Simpson said.
"We get all our kids together for a fun time. Bronx hangs with Maxwell and now Jagger is here they're all interested in her as the little baby. It's very cute.
"Jessica is an incredible mom, so both of us give each other advice. If I have a question about parenting, I'd definitely go to her," she said.