As a canadian, you should immediately file form I-539 to change the status from TN1 to B-2(visit visa)for your whole family. Then mail that with registered mail or UPS etc...whatever the mail give you evidence you mail that.
Then you can wait in USA for either approval or deny of i-539. because i-539 process takes time, so it leave you enough time to handle personal issues, like prepare to leave for canada etc. You kids also can still study during that time.
If you leave usa before the result of i-539 result, Be sure to hand over you i-94 back to us official and show them you have i-539 pend for approval. They will adjust that through internal network
Then you can wait in USA for either approval or deny of i-539. because i-539 process takes time, so it leave you enough time to handle personal issues, like prepare to leave for canada etc. You kids also can still study during that time.
If you leave usa before the result of i-539 result, Be sure to hand over you i-94 back to us official and show them you have i-539 pend for approval. They will adjust that through internal network