So within this year I am moving my family to Sweden. Probably within 3 months. So ofcourse we didn't renew our kids 1 year insurance policy on a monthly plan because Bupa insisted it is only a payment plan for a 1 year policy and we would have to pay all 12 months. I do not wanna be stuck paying after we relocate. I've been searching everywhere with no success. Are there really no companies able to offer a 3 or 6 month plan for my kids?

UPDATE: Situation now resolved. Bupa agreed to 1 months notice on cancellation once we (healthy parents) threatened to also not renew our policies.

Glad to hear you got that resolved, my wife used to have a BUPA policy and there were no problems cancelling that so I thought your predicament in the first post was odd.
I know it's a 12-month policy but they collect the premiums monthly via credit card so cancelling the policy is straightforward.
I'm fairly sure that any BUPA policy can be cancelled without penalty, it's probably just some representative was trying to annoy or lie to you. Shady business practices are par for the course in Thailand!