As an adult I would test if my blood glucose was over 14mmol/l or if I were ill, particularly if I had diarrhoea or were vomiting for any length of time.
Because I very rarely get them and have always been able to get rid of them in a few hours (touch wood)I'm quite happy to use urine strips
but
Some children can develop high levels very quickly and children can't always explain how they feel.
Urine strips show ketones that were developed some time ago . They are sensitive for acetone rather than ß-hydroxybutyrate
which is the ketone most implicated in DKA.
If I were a parent, I were prefer to use blood ketone monitoring. There are a couple of meters that can be used for ketone monitoring. The one I think that is most used is the Optimum xceed. This is a blood glucose monitor that you can buy special strips to monitor ketones with.
http://www.diabetes.co.uk/blood-glucose ... xceed.html