TORONTO -- About 200 parents of children with autism converged on the Ontario legislature Tuesday to demand the government reverse a decision to defund intensive therapy for children five and older.

The issue dominated an emotional question period, with the minister of children and youth services breaking into tears and a parent being forced to leave the public gallery after shouting "liar" and "shame on you" to Premier Kathleen Wynne.

The Liberal government recently announced a new Ontario Autism Program with $333 million in funding, which will integrate Intensive Behavioural Intervention and Applied Behavioural Analysis therapies, currently in two separate streams, into a flexible service that can provide more or less intense therapy.

But the changes include limiting IBI to children between two and four, which Children and Youth Services Minister Tracy MacCharles said is based on expert advice to focus on children in that developmental window.

It will mean 16,000 more children will receive services -- mostly ABA -- and that IBI wait times will go from a current average of 2 1/2 years to six months by 2021, the government says.

But parents say that will come at the expense of children who are five or will turn five in the next year or two, since they will no longer qualify for IBI. The move affects 1,377 children five and older who are already receiving IBI, 835 children in that age group who are on the wait list, and a further 1,331 younger kids who are expected to turn five while they are still on the wait list.

"I am being robbed of seeing my son's full potential to save a buck and to me, that is disgusting and unforgivable," said Kristen Ellison, a single mother of a non-verbal five-year-old boy.

"This is the worst thing that could have happened to our family, short of him getting cancer or dying because I will never know what his true potential was or what it could have been," she said.

"Realizing I may never hear, 'Mom, I love you' is enough to kill a mother inside."

The new program is set to begin in 2018 and in the meantime, children five and older who are being cut from the IBI wait list will get $8,000 to buy therapy on their own. That money would last for 36 weeks of a moderate level treatment, the government estimates. But parents say it's no substitute for IBI, which can cost tens of thousands of dollars a year.

Heather Bourdon decided to enrol her son into private IBI at age four, not wanting him to languish on the wait list any longer. It costs $5,000 a month. The family sold one of their cars, their home and their furniture, used all of their savings and moved the family of five into a one-bedroom apartment to pay for it, Bourdon said.

"So last week when Tracy (MacCharles) and Kathleen (Wynne) said that they empathize, that they understood that this was a difficult transition, I had to ask myself: do they really?" Bourdon said.

"Have they given up all their possessions to uphold the dignity of their child, their child's right to health care and education, basic human rights?"

Both opposition parties hammered the Liberals in the legislature over the changes and MacCharles started crying when she said with a child of her own with special needs, she knows what it can be like.

She said later she is "absolutely convinced" the new system is the best way to get children the most help in the right developmental window.

"They'll transition to a new, enhanced ABA program that will be longer in duration, will be as intense as it needs to be based on clinical assessments," she said. "We need to move away from these IBI/ABA distinctions and make sure we're getting the right treatment for children at the right time."

Both Ellison and Bourdon say their children have received ABA therapy in the past, but to little or no effect.

The provincial advocate for children and youth called on the government to grandfather the children who are already on the IBI wait list.