It appears the web site no longer allows to book tickets for UMs. At least with Aeroplan, I did not check for paid tickets, in which case it would not matter anyway. Whwn you specify children below 12, it won't let you and tells you tht you need to phone.
So, bringing grand kids from YYZ to YYC, I phone in. Then of course, booking fee of $30 each applies, in adition to a tootal of $400 of UM fees, plus some more. When I enquired about the booking fee, agent suggested that I could have made a booking with some phony age and then called in to set up the UM thingy
What a joke... Maybe the web site should say that's the way to do it? :-)