At 5'4", your son probably can squeeze onto a 52 cm frame, but it's not the ideal size for that height.
If he's still growing, and he can handle the standover height with any room to spare, go for it.
He's certainly need a short stem, but that's not the worst thing in the world.
(My frame height formula: cyclist height in inches minus 14 = frame size in centimeters, so his ideal frame size would be 64 - 14 = 50 cm.)
