The games that I played in my childhood.

You can also use "used to" to talk about something that has not continued to the present: "The games I used to play in my childhood."

In the summer, there were many cicadas in the countryside.

There were a few methods to catch cicadas.

You can also use: "There were a few methods (to catching / of capturing) cicadas."

The most simple and easy one was this: prepared a long and slim bamboo first, then took some wheat flour to make "glue."

The simplest and easiest one was the following: I first prepared a long and slender bamboo and then took some wheat flour to make "glue".

When I made the wheat flour "glue", I mixed water and the wheat flour and repeatedly stirred itstirred it repeatedly until it became sticky.

Best to place repeatedly here: "When I made the wheat flour "glue", I mixed water and the wheat flour and stirred it repeatedly until it became sticky."

After the "glue" was done, I grabbed a little bit of the "glue" and attached it to the small and thin end of the bamboo that was prepared before.

You are correct. You can also use: "Once the "glue" was ready, I took a little bit of the "glue" and attached it to the small and thin end of the bamboo that I had prepared earlier/before."

I used my two hands to hold the thick end of the bamboo.

Can also say: "I held the thick end of the bamboo with both hands."

HaveDid you played this game in your childhood?

Best to say: "Did you play this game in your childhood?"

In the summer, there were many cicadas in the countryside.