Theoretical research concerned with the notion of second language (L2) learning difficulty has resulted in specific criteria that can be used to predict the learning difficulty of different languages in terms of both explicit and implicit knowledge. The characteristics of the constructed language Esperanto suggest that this language has lower explicit and implicit learning difficulty than other languages. It may therefore be a suitable ‘starter language’ for child L2 learning in the classroom. Specifically, this paper proposes that Esperanto may facilitate the development of metalinguistic awareness and, as a consequence, boost children’s budding capacity for explicit learning. This would be particularly advantageous in the minimal-input setting of the average foreign language classroom. The paper presents findings from an empirical study which compared 11 to 12-year-old English-speaking children who had learned Esperanto and a European L2 (N = 35) with children who had learned various combinations of European and non-European L2s (N = 168) in terms of their performance on a measure of metalinguistic awareness. No significant differences in overall level of metalinguistic awareness were identified, but the Esperanto group significantly outperformed the comparison group on one of the eleven metalinguistic tasks included in the measure. Moreover, the Esperanto group displayed a more homogeneous performance than the other groups of children. This suggests that learning Esperanto may have a lasting levelling effect, reducing differences between children with varying metalinguistic abilities.