I have a couple of young flute students (10 and 11) who are really struggling to get a strong sound. They able to play with a reasonable tone but can't seem to play above mf. No matter what I say they just do not take enough air in before blowing. I have shown them how to breath properly but they just do not get it. When I learnt to play the flute my teacher went on and on about support etc, but I never understood what she meant. It was only through reading about it in books that I began to understand it myself!

Any suggestions?

You might want to try reposting in the Viva Woodwind forum that tends to be where the instrument specific questions get the best response. With your students you might want to try persuading them to play with their lower jaw positioned further back as they are trying to get louder.

Your pupils are similar age to my daughter, she learnt to play the louder notes with out any problem this was due to the technique she learnt form her Oboe Teacher.