Thanks for your answer. I am currently looking for a validated Spanish version, which I did not mention on the question. Anyway, I appreciate the information.
Perhaps you might use the approach described in the following article, published in 2012: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3343209/pdf/nihms344438.pdf
In the Methods section of this study, the authors wrote: "The BSID-III was
administered in Spanish to those children whose primary language was identified as
Spanish. In these instances, either a bilingual examiner administered the test or an interpreter was used to translate the test items."