We do food challenges eg one summer we tried a different kind of cheese every few days eg Edam, Gouda, Swiss
Get a roll of wallpaper, get them to lie down trace around them and get them to paint themselves life size.
Get outside every day. A walk can be made more interesting by playing a word game as you go. Eg I spy, I went shopping
Swimming
Find out if there is a cheap movie day
Make your own bread or pizza including the dough
Find some chapter books that you think they would all like and read a chapter a day
De clutter their rooms - you can make it fun by playing music, setting a time limit with a timer.
Teach older kids useful skills like sewing on buttons, cleaning the car etc.
Masterchef mystery box for each kid - tailor them to something they can make that is age appropriate eg lemonade, hot fudge sauce