I've observed a number of early childhood classes, where critical literacy is being taught to the students implicitly in terms of what do good readers and writers do - i.e. text deconstruction strategies. I haven't, however, seen this done involving technologies, but I would argue that introducing critical literacy to younger students using the web is an easier task than using offline texts. The reason I suggest this is because students who have grown up being read to, will often take offline texts (including picture books, novels, films, audiobooks) as being definitive representations of what they are being told. Unless the parents are teaching their children to be critical before they enter school, they won't be looking at texts with a critical eye - and this is OK, I don't think students should have to be aware of critical literacy before entering school as in the pre-school stage an enjoyment of reading should be fostered.
The reason I say using the web to introduce critical literacy to younger students is because it is the web that offers so many more examples of falsified information because little on the web is verified. There is a perception that information that is published in books is more verified than what's on the web and that is true to a certain extent, but especially when dealing with fictional texts there are values and attitudes of the author that the reader needs to take into account. I imagine teaching critical literacy in secondary school would be easier to do using print texts, because the students should have a great enough baseline of knowledge and their own critical literacy skills have been developed during primary school.
To relate this back to early childhood teaching (which seems to have inadvertenly become a theme for me!), I think we still need to demonstrate the purpose of reading for enjoyment and interest, which is why I would suggest making the students (even young ones) aware that they are being critical. For instance, students could have a designated reading time where they can pick a book for enjoyment and just read it without the need for critique or analysis and then a specific critical literacy session (or "Smart Readers" session) could bring in online texts to develop these necessary critical literacy skills, e.g. the students might have read a picturebook on space, or they are interested in space, so the teacher finds an online article on alien life on other planets. This could be a text deconstruction activity, involving critical literacy skills and linked to a writing activity (which could be creative or factual). This kind of approach would work for me, with the eventual aim of having students subconsciously assessing texts as they read, with new skills continually being added to the critical literacy sessions.