The paper presents the results of a preliminary research study of inter- and intralingual transfer in young learners' written production in their L3. The research was conducted with Polish-speaking primary school pupils with two foreign languages, L2 English and L3 German. The analysis of the participants' errors indicates that all languages of a third language learner may participate in transfer processes. The language areas most affected by transfer are orthography, morphology and lexis. The observed errors point to the gradually developing meta- and cross-linguistic awareness of young learners, as well as their perception of the typological distance between their languages.