The steps for children to write a letter to Zhan Niangshe Post Office can be as follows:

1. Write an envelope. Write the address of the post and the name of the recipient on the envelope.

2. The beginning. Start with a polite salutation, such as "Dear XXX".

3. Text. In the body of the letter, you can briefly introduce yourself and express your support and gratitude for the work of the post. You can say hello to the soldiers at the post and express your admiration for them. You can also ask about the soldiers' living and training conditions to express your concern for them.

4. Ending. End the letter with a polite closing phrase, such as "Best regards."

5. Signature. Sign your name at the end of the letter and write your age and city.

In the process of writing a letter, you can express your respect and support for Zhan Niangshe Post based on your actual situation. At the same time, pay attention to the format and wording of the letter, and remain polite and respectful.