While you're not allowed to take your twins to a general swimming session at Hereford Leisure Pool, you ARE allowed to take them to 'Adult and Under 8' sessions (whatever that means!):
http://www.haloleisur...s.showPage&pageID=114
I would assume that those session include the Aqua Tots sessions in the teaching pool, from 1130 to 1230 on Tuesdays and Thursdays, or in the leisure pool from 1100 to 1200 on Mondays, Wednesdays and Fridays.
It's also likely that the same policy would apply to the parent & child lessons (but you might have to go on a waiting list to join them):
http://www.haloleisure.org.uk/index.cfm
(Set 'Search for a facility' to 'Swimming lessons')
Chris