The bikes, worth about £320 each, were snatched after being left temporarily at the cafe area on Monday 15th August.
A member of the public saw two men wearing baseball caps and tracksuit bottoms riding away on the bikes between 3.30pm and 4pm.
The bikes were both turquoise ladies Raleigh bikes with low, step-through frames, 24 speed gears and brown gel seats. They had silver handlebars with black grips, silver alloy wheels with black tyres and black mudguards on both the front and rear.
Both were fitted with silver plastic child seats worth £45 each and had serial numbers displayed.
Witnesses or anyone with information about the theft is asked to call Notts Police on 0300 300 99 99 quoting incident number 000239-16082011 or call Crimestoppers anonymously on 0800 555 111.