Simpson added "They are all in such different phases now."
Simpson and her husband, former NFL player Eric Johnson, are proud parents to three children daughter Maxwell, 7; son Ace, 6; and their newborn 3-month-old Birdie Mae, who the couple welcomed in May, reported by Fox News.
The singer shared with the magazine that her youngest baby girl is "so precious" -- especially when she shows off her dimples.
"Birdie is so precious. She is a little smiley angel these days. It is the best thing in the world to see and feel her smile. It fills the room," she told the magazine.
Though taking care of three children can be hectic -- "there is a lot of dividing and conquering going on right now at our house," Simpson said and the couple makes sure that they spend quality time with their children.
"We typically download a movie and order dinner or do something super low-key to just connect. Eric is the greatest motivator and connecting with him on morning walks is the most grounding part of my day," she added.