On a hot day, keep cool by setting up a 'car wash' for all your bikes, trikes and garden toys. Some bubbly water, sponges, brushes and rags for drying will keep the children occupied for hours. If they're really enthusiastic, provide some polish for spoke and saddles too.
On a wet day, set up a dolls' spa in the bathroom instead. A little hair conditioner or fabric softener can work wonders on frizzy, matted dolly hair. And a squirt of WD40 or hairspray and a wet-wipe will remove many marks from plastic dolls' faces & bodies.