Let's look at the sentence you gave:
"Placing them correctly, the child will hear animal noises, learn what farm animals eat and enjoy fun melodies."
Here's how to improve it:
1. The phrase "Placing them correctly" is unclear because it's not clear what "them" refers to or how they are placed.
2. The sentence could be clearer and easier to understand by rephrasing.
A better way to write it could be:
"When the child places them correctly, they will hear animal noises, learn what farm animals eat, and enjoy fun melodies."
This correction makes it clear that the child is placing something correctly, which causes the child to hear the sounds, learn about the animals' food, and enjoy melodies.
Also, don't forget the comma before "and" in a list of three or more items, which is called the Oxford comma. It helps make the sentence clearer.
If you want, you can add what "them" refers to, for example:
"When the child places the animal cards correctly, they will hear animal noises..."
This way, the sentence is clear and grammatically correct!