门前大桥下
In front of the door, under the bridge

游过一群鸭
a group of ducks swam by

快来快来数一数
Quickly come count them

二四六七八
Two, four, six, seven, eight

咕嘎咕嘎
Quack, quack, quack

真呀真多呀
There's really a lot of them

数不清到底多少鸭
I can't count exactly how many ducks there are

赶鸭老爷爷
Old man herding ducks (The documentary Most Dangerous Ways To School - Vietnam for example shows a fantastic example of a person herding ducks on a river in Vietnam)

胡子白花花
with a shinning white beard

唱呀唱着家乡戏
He sings his hometown opera (TODO this deserves further invetigation and examples)

还会说笑话
and he can also tell jokes

小孩，小孩
Children, children

快快上学校
quickly go to school

别考个鸭蛋抱回家
Don't go home with zero points in your exam. (Lit. "Don't bring a duck's egg home", an expression that means to have zero score at an exam, and which here fits in perfectly with the theme of the song.)