31 year old victim taken to hospital after attack on Thursday night.
A Third Of Children Arrested End Up In Court
New figures show out of tens of thousands of children arrested every year - only one in three gets taken to court.
The Howard League for Penal Reform say the figures show an "excessive and inappropriate use of arrest of children".
It warned the situation could deteriorate if police and crime commissioners, which will be elected to oversee forces the first time next year, see children as an easy and popular target to boost arrests.
Frances Crook, the charity's director says "Children are 'low-hanging fruit' which partly accounts for their extremely high arrest rates when the police were forced to work to targets.
In Hertfordshire, 5366 children under 18 were arrested in 2008, 4995 in 2009 and 3948 in 2010.
In Northants, 3096 children were arrested in 2008, 2757 in 2009 and 2594 in 2010.
Across the Thames Valley, 12288 children were arrested in 2008, 10297 in 2009 and 8012.
Both robberies happened within 20 minutes of each other on Wednesday night.
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