Spring:

Xiaoming: 3

Xiao Qiang: 2.

Xiaojun: 1

Xiaohua: 0

Autumn: suppose Xiao Ming made an X cm.

The order may be:

Xiaoming Xiaohua Xiaojun Xiao Qiang

Xxx+2xx-2 is invalid!

Xiaoming Xiaohua Xiao Qiang Xiaojun

X x+2 x- 1 x- 1 is invalid!

Xiaojun Xiao Qiang Xiaoming Xiaohua

X+4 x+2 x X+2 does not hold!

Xiao Qiang Xiaojun Xiaoming Xiaohua

X+3x+3x+2 does not hold!

Xiao Qiang Xiaoming Xiaohua Xiaojun

X+2 x x+2 x does not hold!

Xiaojun Xiaoming Xiaohua Xiao Qiang

X+3 x x+2 x- 1 hold!

So Xiaojun is the tallest.