Middlesbrough. Cost: from £40. E-mail playgroupnetwork@playgroup.fsnet.co.uk or visit www.playgroup-network.org.uk. - 14 May. National conference: Understanding children's play: playing, thinking and imagining. Delegates will hear from speakers including Penny Holland of the London Metropolitan University, Kate Peel of the Qualifications and Curriculum Authority, and Maulfrey Worthington, author and researcher at the Free University...