The Wishing-Chair Again by Enid Blyton

It's the first day of the summer holidays and Peter and Mollie are dying to go on more adventures with their Wishing-Chair. Peter inadvertently asks to go to the land of "Goodness-Knows-Where", but in the process of going there the Wishing-Chair is stolen. They eventually get it back and a few days later, the Wishing-Chair only grows three wings. They end up in the Land of Slipperies and when Peter offends one of them, they retaliate by chopping all the chair's wings off, so they get some ointment which grows the wings back. On the next rainy day, they inadvertently grow wings on their toys and the toys end up at Mr Grim's school where mischievous brownies are sent. They befriend a brownie called Winks and successfully get Mr Grim to relinquish the toys. Winks takes up residence in Peter and Mollie's house and they take him on adventures, but on the last day of the holidays, he is sent back to Mr Grim's school for being too naughty.