Max Davies, who is battling non-Hodgkins lymphoma, was named a 'SuperKid' by his home town and is due to join the free trip to Center Parcs with his 11-year-old sister Lily and parents Sarah and Craig.
But school chiefs refused permission for the children to be absent from classes and threatened the family with £60 fines for taking both children.
The family, from Beighton, Sheffield, were given the free trip to Center Parcs in Nottinghamshire by Amy's Retreat, a local charity which pays for breaks for families affected by cancer.
Max is currently in remission after intensive treatment since being diagnosed in March last year.
The children's schools - Brook House Juniors and Westfield secondary school - say no final decision has yet been made on whether to impose the penalties.
But Sarah told her local paper: "It is great that Amy's Retreat have offered to pay for this break, which they want us to take in term time as it uses up less of their funds.
"But when we approached Brook House they initially refused the time off, saying Max had already enjoyed a once-in-a-lifetime trip in school time when he went to Lapland for a day last year.
"I just wish they'd use their common sense more than anything and show a bit of understanding. We are going to refuse to pay fines if they are imposed."
Brook House head Mark Hinchliffe. and Westfield head teacher Andy Ireland. issued a joint statement, saying: "No decision has yet been made by both schools about whether the family will incur a fine for an unauthorised school absence following their trip to Center Parcs.
"However, both schools are guided by the Government regulation relating to term-time holidays, and we would support the principle that all children should attend school consistently so they can benefit from the learning we provide."
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