Given the increasing use of app books with young children, research is needed to inform their selection and design. Although broad guidelines exist, more fine-grained guidance is needed. To address this need, we explored the relations among app books' digital affordances, readers' behaviors with these affordances during both buddy and individual reading sessions, and their individual outcomes. Fifty-three kindergarteners (ages 5.05-6.46 years; M = 5.60, SD = 0.42) read 12 app books twice each across 24 buddy reading sessions and four app books once each across four individual reading sessions, and their comprehension was assessed after each individual reading session. Multivariate, mixed response analysis found that (a) when a greater number of minimum hotspots were available per page, retelling was better; and (b) availability of word hotspots was linked to better critical thinking/inference outcomes. Implications include choosing app books with affordances that this study showed support particular reading outcomes, in alignment with instructional goals.