Theory:

“Fall?” scoffed Dad,
“A climber like me?
Child’s play, this is!
You wait and see.”

He got out the ladder
From the garden shed.
It slipped. He landed
In the flower bed.
Explanation:
 
In the third Stanza, the child's father began to implement his Plan A with overconfidence, calling himself a good climber and insulting his wife. Climbing a tree, he says, was like "child's play" for him.

Stanza \(4\) describes how he rushed to the garden shed to fetch a ladder. He used it (the ladder) to go to the top of the tree. Nothing worked out. As his wife suspected, his attempt failed and he fell on the ground. His wife had already warned him not to climb the tree since the branches appeared to be frail and unstable. He didn't pay attention and ended up on the ground.
 
wallpaper-3898967_1920.jpg
The Kid's father uses ladder to climb up the tree
 
Meaning of difficult words:
  
S.No
Words
Meaning
1.
Scoffed
Mocking at someone or their idea
2.
Mock
To laugh at someone or something
3.
Over-confidence
More sure of oneself than one should be
Reference:
National Council of Educational Research and Training (2007). Honeycomb. Dad and cat and the tree - Kit Wright (pp.107-109). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.