The first level of reading critically is understanding basic facts. Play treasure hunt games with written clues to evaluate the children's current level of reading comprehension. Design the clues so that they must be read carefully and interpreted correctly to find the next clue. Use words they know and understand but also include one or two new words, which forces the children to think about the context of the word and interpret according to the information they have and understand.
Play "Simon Says" games with written commands. If the commands are executed incorrectly, the player is out or loses points. Incorporate a variety of commands and writing styles to encourage critical reading and comprehension. This also helps with basic reading comprehension.
The next level of critical reading skills goes beyond understanding facts and instructions to thinking and analyzing not only the words but the ideas, philosophies and worldview behind them. Read aloud with small groups of children. Have the children take turns reading aloud, then pause to discuss the meaning of the text. Encourage a deeper discussion beyond the words to ideas behind them. Allow the children open opportunity to speak, but facilitate the discussion to ensure that the final analysis is correct. Determine the tone and purpose of the text, any biases and the conclusion to which the author draws the reader.
Writing will cause children to think more carefully about the process of reading as they craft their own ideas into words. Give writing assignments to children and when they're done, have them hand their writing to another child, who then reads and interprets what they have written. Ask the writer if the child has interpreted correctly what they meant to say. Writing enforces critical reading and thinking skills and will help them understand the process behind the texts they read.