Streaks, the number of consecutive days people have sent Snapchat messages to each other, should be dropped, she told the Telegraph.
She also pinpointed autoplay videos and algorithms that identify interests to serve youngsters with more content.
Snapchat said its streaks were not designed to encourage addiction.
In an interview with the newspaper, Ms Longfield said: "I would like all these to be looked at and really reduced down, if not taken away.
"The internet is set up to be addictive. All of the algorithms on it are silently working there to keep us addicted, whether it is the little dots that come up to tell you someone is writing a reply, to the YouTube video that moves on to the next in a nanosecond."
A Snapchat spokesperson said that Snapstreaks were designed to allow friendships to deepen over time and were meant to be light-hearted and fun.
In recent updates, the streaks indicator has been made smaller to make them less of a focus, the spokesperson added.
The UK's Digital, Culture, Media and Sport Secretary Matt Hancock does not allow his own young children to have mobile phones.
The Children's Commissioner's words also echo those of Health Secretary Jeremy Hunt, who said earlier this year that spending too much time on sites such as Facebook could pose as great a threat to children's health as being obese.
He has met with executives from Facebook, Twitter, Snapchat, Google and Apple to discuss the issues.
He asked them whether they could provide evidence of what constitutes too long online and whether they can provide ways of alerting children who have exceeded that amount of time.
Since the meeting, Apple has introduced Time Limit in its latest operating system. This will allow users to pre-determine how much time they should spend using individual apps and setting off an alert when that allowance is used up.
And, at its developer conference, Google also focused on moves to reduce screen-time, with pop-ups on YouTube telling youngsters to "take a break" after a certain amount of time, pre-determined by parents.
Source : https://www.bbc.com/news/technology-44452265