Napo claims changes to the Legal Aid, Sentencing and Punishment of Offenders Bill, will not achieve the intended results.
The bill includes provision for an increase in fines levelled to children breaking the youth rehabilitation order from the current £250 to £2,500.
Harry Fletcher, assistant general secretary of Napo, said all those affected will be under the age of 16.
"The only way they could pay the fine themselves would presumably be through a massive increase in their involvement in crime, or it would fall to their parents to pay.
"In the event of the money not being given to the courts, presumably the individual young people or members of the family would be jailed in default. To increase fines for young people who breach their orders by tenfold is patently absurd."
The bill is due to go to committee stage in the House of Commons next month.
