What telly does to toddlers
Next, two bits of more worrying news: no one is yet sure about the effects of too much TV on the under-twos; and for all young children there's considerable difference between the effects of "appropriate" and "inappropriate" viewing.
A research report by Dr Robin Close for the National Literacy Trust found a surprising dearth of research studies about the under-twos. What there is, however, indicates that they learn much more by interacting with adults than from watching television.
Once they've begun to talk, shared viewing with adults can provide a focus for vocabulary development - and the frequent repetition offered by video means young children often imitate songs and speech from favourite programmes.
But for the growing number of under-twos who have a TV in their bedrooms (recent research in the United States put this at 26 per cent) lone viewing may be doing more harm than good.
As more than a third of four-year-olds in the UK now have a TV in their bedroom (and this number is increasing year on year) it is likely that many of the children in the two to five age group are also viewing alone, or possibly with siblings.
If they have a normal level of language development and are watching age-appropriate "educational" programmes like Nickelodeon's Blue's Clues or CBeebies' Tikkabilla, their language is likely to thrive - although Dr Close's survey showed that shared viewing of such material with adults was even more productive.
However, too much inappropriate TV (programmes aimed at older children or a general audience) may actually inhibit language development - and this seems to be a particular problem with boys. The presence of older siblings can also mean that young children are denied access to programmes that benefit them.
This review provides many helpful pointers for parents and teachers, but if we are to learn more about how the huge social phenomenon of television affects our children's future capacity for learning, we really need a lot more focused research.
Television and language development in the early years: a research review by Dr Robin Close is available on www.literacytrust.org.uk. Sue Palmer is an independent literacy consultant and writer