Insurance for status update from H1 to F1

[submittedviaemail]

Hi
Currently i am on H1b visa and applied for college and the classes start 1/19/17 and i will be applying for H1 to F1 status update in few days so can i buy F1/F2 insurance starting today/tomorrow also i have 2 kids who are US citizens can i want them to be covered under my policy in the application it dosent give me an option to select US citizenship for my kids

Please let me know at the earliest how should i proceed

Regards,