The present study discusses and describes codeswitches produced by two trilingual children acquiring English, Spanish and Hebrew simultaneously from birth. Data were collected regularly over a period of 20 months (from age 2;6 to 4;2 for M and from age 5;5 to 7;1 for E), in naturalistic tape-recorded sessions. Codeswitches drawn from transcriptions of 32 h of spontaneous conversation were analysed. We describe and explain trilingual switches involving morphosyntactic boundary violations, some of which have not yet been reported in the literature. We claim that these switches provide incipient evidence for a developing trilingual competence that stands at the base of trilingual performance. (Contains 8 tables.)