As hollow reeds and straws have been available for a very long time, and soap as well, this simple pastime could be hard to date. In his classic book, the scientist C.V. Boys stated that there was an Etruscan vase on display in the Louvre that showed a boy blowing soap bubbles. He also stated that he didn't know what brand soap they were using ( Boys was a genuine Victorian eccentric). But I am not able to verify this, and as Boys got his citation from someone else, it's possible they simply mistook a boy playing the aulos as blowing bubbles, like this one https://en.wikipedia.org/wiki/Etruscan_vase_painting#/media/File:Estamno_de_Etruria_(M.A.N._Madrid)_01.jpg

Much, much later there is a very well-known 1733 painting by Jean Siméon Chardin of a boy leaning out a window blowing bubbles with a straw. But all sorts of people had been interested in them before then. Isaac Newton used them to study the interference of light, and managed to figure out their thickness ( about 0.00001016 mm)

Boys, C.V (1889) Soap-Bubbles and the Forces that Mould Them