It's actually 80p for under-18s. All this information is in the fares
leaflet, for which a link is provided on the web page you referenced
(though they got the page number wrong, it's page 20 of the leaflet =
page 11 of the .pdf file).

I had a feeling it was a group ticket, but when I looked on the Pdf I
couldNt see anything on the section they referred to. Thnks very much.
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