When children are aged around 2 years, many of the early foundations of mathematical skills are developing. Understanding this is important to shed light on theories of mathematical development. Nevertheless, little research has investigated 2-year-olds' early mathematical abilities, with most research focussing on either infants (aged 0-1 years) or pre-schoolers (aged 3-5 years). One possible reason for this lack of research may be the challenges associated with the methods used with this age group. Here, we review the methods used to assess 2-year-olds' basic mathematical skills and identify the gaps and issues with those methods. Our findings indicate several issues, both with individual methods used to test specific skills but also some common challenges applicable across all measures and skills. We discuss the identified issues and highlight a need for more appropriate approaches and for alternative methods of administration to better evaluate 2-year-olds' mathematical skills.