The children all go to Earls Barton Primary School and are due to move up to Wrenn Academy secondary school in September, using the council-operated bus service to get there and back.
But a letter from County Hall has now told parents that only children who attend their nearest secondary school get free places - and contrary to what it told them in March, that is now deemed to be Weaver's.
The review - conducted using Google Maps - means the free bus places have been withdrawn and the journeys will now cost Â£600 per child per year.
Parents have told this newspaper that they are seething, particularly at the tiny distances that have led to the change.
Kay Smart whose - who is already at Wrenn's but will, bizarrely, be unaffected - said: "I was absolutely disgusted when I read the letter. We checked and Weaver's is nearer the two schools by just 300 metres.
"The worst thing is, my daughter and the other children have been confirmed as going to Wrenn's since March, along with their confirmed free bus places. What are they doing conducting a review of those children a few days before the school holidays?"
The county council apologised for the error, but a spokeswoman said it was unlikely the decision would be reversed in case it set a precedent.
She said said: “Secondary age pupils in Earls Barton receive free home to school transport to Wollaston School, or to Weavers School or Wrenn School, depending on which of these two schools is closer to their home address.
“Free home to school transport is only available for secondary school pupils to their nearest suitable school where the distance is over three miles and in this case, the family does not qualify for free transport.
“Unfortunately this family was advised in error that they were eligible for free home to school transport and we sincerely apologise for the misinformation.”