Hello learned community of Skywards members!

I am keeping an eye on upcoming award availability ex-DXB to pretty much anywhere in Europe/UK for the return leg of an upcoming trip with my 10-year-old son. We're aiming for 2 x F rewards, and are being flexible on date and route in order to get something. I read through the discussion on infant (ie. under 2 years old) redemptions, the 10% rule, economy only. cash+miles for upgrades etc... however was presented with this error message when browsing through availability:



The 'not enough miles' point I can deal with easily through an Amex transfer, but the 'Economy only for child passengers' point threw me. I can't find any trace of Economy-only award bookings for children (as opposed to infants) mentioned in the Skywards T&Cs. Is this just plain incorrect? Any experience?