Make sure your child spends as much time as they can spare doing some outdoor activities especially during day time.
2. Your child should avoid using a phone, laptop or any other digital device and should only use them when it's absolutely required.
3. There are commercially available spectacle lenses that as per studies show and give us upto 60% control over the increase in number.
4. Some eye drops proscribed by your doctor offer some control over increasing number in some cases.
All of the above options either individually or in combination can help you control the increasing number to some extent but should be advised after a checkup by your doctor.