How do they know they are children? At those ages, the ticket prices are going to almost always be the same as yours, so how exactly is the airline doing this to you deliberately because you have kids in the party? (The only tip-off I can think of offhand would be if you were requesting special childrens' meals on long-hauls. They are too old to be using carseats.)

Personally, I think that it is most likely happening not because you have children with you, but because you are a party of at least 4, are travelling on a discounted leisure fare, and/or have very little FF status. I'm guessing you are also insisting that you all sit together?

The front of the plane very seldom has large blocs of seating available, because business travelers with status are going to be filling the aisles in the first 10-12 rows. Booking way ahead won't help, as the best seats are often held open for status passengers until just a few days before departure, and on legacy carriers the equipment is likely to change on you anyway. Also, "leisure" fare seats are sometimes restricted in terms of seat location for preassignment.

If your husband has status, you may end up nearer to the front of the plane if he is flying with you and if he is the passenger of record on the itinerary. However, if you need 5 seats in a bloc, you're probably still going to be behind the wing.

You might try splitting the reservation into a party of 3 and a party of 2. Your odds of getting spots forward of the wing are better with smaller groups.