The work raises problems about the possibility of extrapolating the effects of bilingualism to trilingualism at primary school age, about the increase/decrease in cognitive regulation in bilingual children in the process/result of their acquisition of other languages. The purpose of the pilot study is to identify opportunities in cognitive regulation among primary bilingual schoolchildren in the educational situation of learning a third language. The study involved second grade schoolchildren (N=60) aged from 8 to 9.8 years (M=8.8, SD=0.36), among them with unbalanced bilingualism (N=30, 15 boys, 15 girls ) from the national Udmurt gymnasium; monolinguals with their native Russian language (N=30, 13 boys, 17 girls) from a secondary school in Izhevsk, Udmurt Republic. To measure the components of cognitive regulation, the following were used: test battery NEPSY-II (children's version in printed form): “Repetition of sentences”, “Memory for construction”, “Inhibition”; computer test samples of the software of the psychologist's toolkit “Practice – MSU”: Stroop Test, Shulte Tables, Memory for geometric shapes, Go-NoGo. The main statistical method for analyzing empirical research data is structural modeling (structural equation modeling). The results of the pilot study show a possible syncretic (mixed) effect of bilingualism in the process of mastering a third language by primary schoolchildren with the need to control it in the educational situation. We assume that bilingualism in the educational situation of learning a third language, as a predictor of cognitive changes, provides advantages in the self-organization of subsystems of regulatory processes at the cognitive level and, at the same time, creates difficulties due to the high regulatory load.