Although I dont have any I would think it is a great thing to do with kids, you get them out the house going on a hunt for something that noone knows where it is!
www.geocaching.com is the site, just sign up and whack your postcode in within any distance you want from the house. You will find the caches are all rated between 1-5 for difficulty and terrain, ie a 1-1 will be very easy to find and should be on or within reach of a footpath whereas a 5-5 may be a puzzle up a tree. The maps are powered by openstreetmap so can overlay cycle maps and each cache usually says if it can be reached by bike (although various attributes are not always added)
You will prob be suprised at how close you are to one! I think the closest to my house is around 450m or so.
Infact to get an idea of whats about you dont even need to sign up, go to play>hide and seek a cache and then add the postcode, you wont get the exact location (to stop anyone just going to it and taking it away) but it will give you an idea if you wnat to have a go!