An article on child acquisition of the ergative forms in Basque finds that Basque children receiving bilingual input, i.e. two different languages being used in the same household (Basque and Spanish) are slower in acquiring the appropriate forms and distribution of ergative syntax than are children who hear only Basque as input. The reason surmised is that the latter receive more input, i.e. repetition of those forms.
TPRS urges many repetitions of what it calls “structures” to insure acquisition.