"Sure we can," the boy said.
"I will" said the girl.
"I don't like that park" said his brother.
Is it correct to use "said" in each of those sentences? Sure! But can your writing be more colorful and exciting with alternate words? Yes!
"Sure we can!" the boy exclaimed.
"I will" answered the girl.
"I don't like that park" the boy said sheepishly. (I know, I used said... but only once)
In the world of technology, we forget about good old fashioned BOOKS! (present company included) I initially thought to look up an app that is a thesaurus. However, I decided against that. Kids need to learn to physically look up a word in a thesaurus to see what other words they can use.
If this is an area where your child struggles, I would start by reading. Point out the different use of words around quotations. I think that's the easiest place to start. It stands out to the child because of the quotation marks. One book that does a great job of this is "Time To Sleep" by Denise Fleming.
After you have pointed out the different words that can be used, then I'd have your child create a book, write a short story, or use something he/she has already written. Focus on one word. Have your child LOOK IT UP in a thesaurus to find alternate words that can be used. Have him/her "sprinkle" those other words into his/her writing. Again, beginning with quotation words can sometimes be the easiest place to start.