(I editorialized some of this to make it generally easier to read. You can consolidate shorter sentences into slightly longer sentences with more information. This reduces redundancy. Also, I changed "flour" to "powder" since that was one of the themes. If actual flour was used I wrote an alternate sentence.)

Yesterday my family and I went to the Yeonsu Art Hall for Children.

My wife made a reservation for our children to participate in an activity called "Powder, Tree, Sand, and Soil".

For the first activity, children can draw pictures through powder using their fingers or a brush. 

[or: For the first activity, children can draw pictures through flour (to represent powder) spread across the floor using their fingers or a brush.]

Next, they can make rainbows in a bottle using colorful sand. They can also try to discover toy jewels buried in the sand. 

Then for soil, children can make things with clay and paint their parents' bodies with muddy water.

The final activity is about trees.