There are a number of resources which can be used to teach children about speech marks:
1) Witch and Tiger Conversation. This worksheet (in PDF format below) shows ten pictures of a witch and a tiger having a conversation. The speech bubbles are blank, and the procedure for using this worksheet goes as follows:
First, the children can choose names for the witch and the tiger.
Then, they have to create the contents of the conversation. The topic of the conversation could be decided by the children, or it could be based on a choice by the teacher. You could even complete the conversation before the lesson, in order to save more time for the next (and most important) section.
Now the children have to re-write this conversation in the form of a story. They will need to include phrases such as "said Tom" and "asked Joe". Speech marks will also need to be used, so it is important that children have a good knowledge of the correct use of speech marks before this activity is tried.
2) Missing Speech Marks. This activity is also based on a worksheet, which can be also be found below. It contains a number of sentences involving speech. However, the speech marks have been removed from the text and should be replaced by the children.
3) Missing Speech Marks. This activity is very similar to the one above, with children required to put speech marks in the correct place in each of the sentences. The worksheet (in PDF format) is also below.