Picture of activity
In addition, the newest trackers go beyond counting steps to monitoring sleep duration and quality, as well as creating a graph of active and sedentary time. Those features could help families become more aware of their kids' activity levels, Garrison said.
"Some things that increase physical activity in the day aren't always what we expect," Garrison said. "It may not be soccer practice, it may be helping dad and mom with chores around the house."
Garrison is conducting a small pilot study to see whether a FitBit device can help obese children and their families become more aware of when children are most active. The hope is that by focusing on mindfulness, as well as having family members work together to improve their fitness, the trackers can have more long-lasting effects on health, she said.
Using a fitness tracker doesn't require extensive commitment or sophisticated knowledge, which could be a hurdle for families where obesity or inactivity are problems, said Bethany Soule, the chief technology officer and co-founder of Beeminder, an app aimed at motivating people to change their behavior that works with multiple fitness trackers.
Unlike counting calories or manually tracking activity with a paper chart, "you don't have to know anything about sports or how to exercise or use a gym, you just need to move and here's a little device that tells you how active you are," Soule said.
No perfect device
Despite several startups focusing on fitness trackers for kids, companies are still struggling to come up with the best way to design them, Garrison said.
Soule and Daniel Reeves, the CEO and co-founder of Beeminder, for instance, have found that none of the fitness trackers are a perfect fit for their children, ages 5 and 6.
Given how pricy the devices are often costing more than $100 it can be hard to justify the expense for children, who are likely to lose them, Reeves said.
Many trackers must be charged frequently, and some require users to physically connect the tracker to a phone or computer to see their data, which is hard for children to remember, he said.
Ideally, a tracker should have a way for kids to instantly see the data, while also giving parents access to it, Reeves said.
Trackers may also underestimate children's sleep, said Lisa Meltzer, a pediatrics professor at National Jewish Health in Denver, Colo.
Most fitness trackers use tiny accelerometers that measure motion, and label any period where a person is holding still as sleep.
"The problem with this is that children are very active sleepers, moving a lot during the night," Meltzer told Live Science.
So although sleep data from these devices might provide some insight for instance, letting parents know if a late bedtime is affecting a child's mood the next day, or if children are getting up earlier than thought they shouldn't take the total number of hours of sleep as accurate, she said.