Two works by Drouais, "The House of Cards" and "Blowing Bubbles", were included in the estate sale of H. L. Bischoffsheim, London, held at Christie's, London, May 7, 1926, nos. 30 and 31, ill., but auctioned as one lot for the high price of £13,650. Number 30 is an oval canvas, signed and dated "Drouais le fils 1766," measuring 28 by 23 1/2 in. (71.1 x 59.7 cm). The boy's costume is described as a yellow coat with white frills and blue sash and a felt hat with blue and white ribbons. Number 31, an oval of the same size, is signed and dated "Drouais 1767." The girl is said to wear a blue dress and a black hat tied with a white ribbon. The buyer, listed as Smith, was Wildenstein.
Presumably these are the pictures that were engraved by Marie Louise Adélaïde Boizot (b. 1744). See Marcel Roux, "Inventaire du fonds français", vol. 3, "Graveurs du dix-huitième siècle", Bibliothèque Nationale, Paris, 1934, p. 125, nos. 8, 9. Her black chalk drawings for the engravings were sold with the collection of M***, Hôtel Drouot, Paris, May 23, 1899, no. 22.
It is likely, though not absolutely certain, that the "Boy Building a House of Cards" that was on the London art market in 2001 is the Bischoffsheim picture. Certainly the palette is the same. The pendant may belong to a member of the Rothschild family.