Maybe they are children’s books, for the kids to look at so they won’t make noise during the liturgy. Might test them for crayon residue but if they were coloring books, probably too much time has elapsed and none of the crayon residue has survived.
Trivia Time: Encaustic painting, which is done with the pigments suspended in hot beeswax (i.e. old fashioned crayon) is one of the most durable media out there. Here's one from about 100 years before Christ...