This paper reviews the key types of personalization in children's literacy apps to propose a taxonomy and research framework for future empirical studies Systematic content analysis was used to identify the amount and type of personalization in a hundred most popular children's literacy apps/digital books. Titles with three and more personalization features were screened qualitatively to identify what can be personalized, how personalization occurs and who personalizes the experience. Similar themes were synthesized into a research framework that outlines how identity, self-evaluation and agency relate to personalization. The discussion sets the agenda for future research, design and evaluation of children's digital books.