Shortly after Brown's results were published, Dulay and Burt (1974, 1975) reported that children acquiring English as a second language also show a "natural order" for grammatical morphemes, regardless of their first language.
(For a review, see Dulay, Burt, and Krashen, in press. Ravem, 1974; Milon, 1974; Gillis and Weber, 1976; Cancino, Rosansky, and Schumann, 1974; Wode, 1978 and Nelson, 1980 are some second language studies in this area.) There is surprising uniformity here as well--acquirers make very similar errors, termed developmental errors, while they are acquiring.