In the following year, he adopted James's eldest son, William Henry Playfair, then only six years of age. William would follow in his father's footsteps and also become an renowned architect.
Sa mga sumusunod na taon, siya pinagtibay James's pinakamatanda anak na lalaki, William Henry Playfair, pagkatapos lamang ng anim na taong gulang ang edad. William ay sundin yapak nang kanyang ama at ding maging isang matunog na arkitekto.