ItsInning - couple of ideas for those long damp childlead days !
Libary - many have websites, some have classes / activities for the little ones, reading groups from 8years for older ones.
Discovery centres - some bigger town libaries have bloomed into discovery centres, child activities here can cost but even without these an hour or two can be passed warmly, browsing, reading aloud in a corner with children, looking at gallery etc.
Nature reserves - look on local council website for activites at local green spaces, walks and talks and other bits and bobs throughout the year, often free and always looking for volunteers for a bit of pond clearance, tree planting etc, take own drinks and snacks, can get warm whilst working and fill a morning.
Bus travel in holidays - often bus companies run £1 offers for children, plot a short route and times and bung kiddies on a bus tour, stretch activity by giving older children use of cameras and video phones they can make a nice little project out of this, for younger ones its great to get them reading road signs etc.
If you find the draw of coffee shop still pressing try eating a ceral bar (£1 for 6 at Lidle) before you go in, then have s small full fat latte when your in, the combination will make you feel surprisingly full, always get your loyalty card stamped if they have one, for children if they are small enough take sippy cup drinks for them (no-one would object to this) for older children give them a financial choice ie you can have a milkshake for £3, or £3 in your moneybox,or small toy for the same, or smaller drink, or share a drink and save half etc - children can spend an inordinate amount of time picking throug options and discussing this one - meanwhile sit back and enjoy your coffee.