The phrase "to lift the flaps" means to pick up or open a covering that is usually attached to something, revealing what is hidden underneath. Full definition
Then have children lift the flap and glue inside their more recent picture (s). (educationworld.com)
Then have children lift the flap and glue inside their more recent pictures. (educationworld.com)
Just pop your family photos (or other pictures that your baby loves) into the vinyl pockets and he'll have great fun lifting the flaps on each page to see who's underneath! (homemade-baby-food-recipes.com)