This is one of my favorite, yet heartbreaking, facts of the year. If you haven't been to the Isabella Stewart Gardner Museum yet, it's a great outing - not to mention a fantastic museum - and I highly recommend visiting when the doors open once again. Until then, a Google Tour will suffice.
May I suggest exploring more about Isabella Gardner, listening to Last Seen the WBUR/Boston Globe podcast about the heist, and exploring more about Vermeer and Rembrandt. There is also a mini-series on Netflix that outlines all of the theories behind the heist and where the artwork may be. In 2015, CBS 48 Hours did an in-depth report on the case and followed many of the leads.
The children's book Chasing Vermeer by Blue Balliett is a fantastic mystery about a different Vermeer painting, it is largely set at The Art Institute of Chicago (my old stomping ground).
For adults, An Object of Beauty by Steve Martin incorporates the Gardner heist into its plot, and the novel Girl with a Pearl Earring by Tracy Chevalier give a fictionalized account of the girl who posed for the famed painting (it's also a movie). The documentary movie Tim's Vermeer is a fantastic exploration into the science and math of art, and is appropriate for all audiences.