This is one of the popular Ruth Chew books on magic and witches for younger children. She wrote and illustrated the texts with beautiful charcoal drawings. From the back of the book:
One minute she's there--the next minute she's gone!
Marjorie and Nick are sure they see a witch standing on the air conditioner outside the window. Then she disappears into thin air!
That's just the beginning of some strange adventures for Marjorie and her brother. They meet a talking bird and then find the witch's book of magic spells. They can't wait to try the spell that will make them invisible....
Marjorie and Nick are about to learn that magic can be a very tricky business.