The five mums were given the green light to sell chocolate bars, sweets and milkshakes to raise money for their children to go on a trip with their former primary school.
But a dinner lady, who did not want to be named, claims pupils are filling up on sugary snacks and turning their noses up at healthy school meals.
She said: "We are not allowed to sell chocolate to the children because of the new healthy regime.
"These parents are buying the sweets and chocolate at bargain prices and selling them at full price.
"The children are not coming in for their dinners any more.
"Today our sales were down by half – we had about 30 pupils for dinner.
"We are there in the morning slogging our guts out and they are eating Kit Kats.
"If there is meant to be healthy eating in schools, like the Government stated, then they should stick to it."
Now, the School Food Trust, which recently recruited supercook Prue Leith to help them fight for healthy eating and food training in schools, has waded into the argument, criticising parents for undermining the healthy-eating drive.
A spokesman for the trust said: "It's a pity the best intentions of parents seem to be undermining the healthy-eating drive at the school. What is the point in the Government pushing healthy eating if the school dinner take-up has dropped because children are filling up on junk food paid for by their mums and dads?"
But Halifax High head teacher Jeremy Waxman defended his decision to allow the mums to sell the snacks because he says it is for a "worthwhile cause".
Mr Waxman said until September schools were within their rights to sell such confectionery, and the stall is temporary until the mums raise £2,000.
He said: "They sell books and confectionery such as Werther's Originals, Time Outs, Snickers, banana-flavoured milk drinks, mixed-fruit drinks and Just Juice, as well as apples, bananas and satsumas.
"I said no to cans and crisps, but I think to nitpick over confectionery would have been demoralising to them.
"I am proud of what they are doing because it a very exciting and educational trip for their children.
"I support healthy eating but I do not think small amounts of confectionery are damaging youngsters' long-term health.
"If they were relying on it for their daily intake it would be unacceptable, but this is short term.
"Other schools still have vending machines selling this type of stuff and we don't have any of those."
Mr Waxman said he was "keeping a close eye" on the stall and the children were buying fruit from it, which was more prominently placed there than it was in the canteen – run by company Rentokil Initial.
He said it was a better alternative to allowing the children to visit local shops at lunch time, where they could fill up on junk food.
"I think we should control what is sold in schools, but have some leeway," he said.
"I would be interested to hear how rigorous people think health guidelines should be in school.
"Should they be 100 per cent or room for margins?"
Last September, mums from Doncaster hit the headlines for passing fast food through the gates to pupils at Rawmarsh Comprehensive School.