On a rainy day let your children make their own frames for portraits of friends or family. Mount each photograph on stiff cardboard with double-sided adhesive tape, leaving a ¼in/6mm margin all around. For a frame, glue wooden pencils to the margins.
To make random frames look like a set, spray-paint them all one colour or use coordinated mounts.
Reinforce a wobbly frame with a staple gun; drive two staples across the back of each mitred joint.
Scout junk shops and jumble sales for framed pictures. You may not like the pictures themselves, but the frames might be attractive. just remove the old picture and then clean and paint or wax the frames before reusing.