Validity of Kids Visa

I exited country on visa cancellation without NOC in Oct 2014. My children who are in hostel were in hostel that time (they left in June 2014 for hostel)  did not surrender resident card when they left bcz they had gone in summer.
My wife is still in Oman on a separate work visa and kids would like to visit during winter vacation.

I was told at the time of exit that dependent /kids visa would be valid till 6 months after my exit date and kids can come back during winter holidays in Dec on same resident card.

Can they visit Oman on their existing resident visa ?

Someone please clarify!