As a frequent flyer on Midwest (and I do really love this airline), I can only offer the reason the change took place. Just recently (probably after you had made your ressies, Vija), Midwest changed the 5 routes more traveled by vacationers (Orlando, LA, Phoenix, Denver and Las Vegas) to the more common 2 and 3 seating, leaving all their other routes, more traveled by business travelers with their 2 and 2 seating. And they lowered the fares quite dramatically. When I was checking earlier in the year for Dec (still priced at 2 by 2 then), the fares were in the mid $200's. When I made my Dec ressie, the fare was $192. And, with checking every so often for even better, I did catch it at $176 (now back at $192) and received a $16 voucher. The seat pitch (distance between seats, back to back, is the same, though about 1 1/2 inches narrower.
I think when the flight was reprogrammed from 4 across seating to 5 across, Vija, your family was 'computed' in a non acceptable manner for young kids. I have almost as much joy in dealing with Midwest employees as I do Disney CM's, I really think they are great. Call again, Vija, and explain your situation, I am sure they will listen. Others were randomly reseated too, and can be again.
I live 5 minutes from O'Hare, yet always go to Milwaukee, staying overnight the night before at Four Points, leaving my car there and using their shuttle service to and from the airport. I love it.
Also, Vija, check the current rates and see if your fare is lower. If so, ask for vouchers.
If you have ANY questions or concerns, PM or eamil me.
Dan
PS: I do not work for Midwest, LOL.
