[jimworcs]

It is undoubtedly the OP's fault in this case, and it is a bit much to be blaming Air Canada staff. It sounds like they tried t to assist you, but these are government rules. It may seem stupid to you to have to have a visa to transit, but many countries have this rule. (The US is one of them). There are numerous complaints on this board and others where people have misunderstood the rules and then blamed the airline.

The London/US route is probably one of the busiest international air corridors in the world, and the OP would have been well advised to have changed in NY or taken direct flights to BWI, Dulles via BA or even on the dreaded US Airways. Presumably price was a factor in choosing to travel Air Canada.

I do think the change fee in these circumstances might have been "waived"... but it was relatively modest. I am sure if it was Delta that would have cost the family at least $150 change fee per ticket, plus the difference in price between the ticket price on the day and the advance purchase ticket they bought. For 4 people, I am guessing that little mistake would have cost them thousands.

So, undoubtedly a stressful and uncomfortable day for the OP, and one that cost them a bit of money. But certainly not Air Canada's fault.