Judgment of the Court (Sixth Chamber) of 3 May 1990 in Case C-2/89 (reference for a preliminary ruling made by the Centrale Raad van Beroep, Utrecht): Board of Management of the Sociale Verzekeringsbank v. Heirs of and/or successors in title to Mr G. J. Kits van Heijningen (Social security Jbr migrant workers — Part-time worker — Family allowances — Council Regulation (EEC) No 1408/71 — Article