Kate Fisher, 22, and her partner Alex Gleghorn, 24, said Matilda's was only diagnosed with brachycephaly, a form of plagiocephaly (commonly known as flat head syndrome) at a year old.
Matilda and her twin brother were born prematurely – a contributing factor to the condition which is common in twins.
Kate, of Greenside Road, said Matilda's head was visibly flattened at the back and bulging at the side.
She said: "From birth I noticed her head wasn't right. The doctors said it was just the shape of her head and said I was comparing it to Harry's. They said she'd grow out of it."
By the time she was referred to a specialist at 14 months, the family was told she was too old to be treated on the NHS and they had to turn to private treatment.
Seventeen-month-old Matilda now wears a plastic Starband helmet for 23 hours a day and after two months of treatment, she is making good progress.
Kate has set up an internet group and launched a petition to get the NHS to fund treatment for plagiocephaly.
She said: "I want more information to be on hand if you are faced with your child having this condition. The NHS should fund this treatment so it doesn't affect a child in later life."
Batley couple Tina Davies and Carl King are backing the campaign after the success of their five-month-old son Liam's private treatment.
Tina, 23, said: "I don't know if it's that doctors don't know about it or they're just ignorant to it but it should be so much more known about.
"Liam's treatment's finished now and within two months his head shape changed by 10mm and it's going back to being round."


To sign the petition log on to http://petitions.pm.gov.uk/Plagiocephaly/ or call into the Reporter office from midday today.

The petition is also available to sign at:

Halo Hairdressers - Town Hall Street, Mirfield
Browns Hairdressers - Calder Road, Mirfield
Maze N' Jair Restaurant - Huddersfield Road, Mirfield
Hairheadz - Old Bank Road, Mirfield
Post office - Greenside Road and Huddersfield Road, Mirfield
One Stop - Greenside Road, Mirfield
Ashcroft Fisheries - Sunny Bank Road, Mirfield
Old Bank Fisheries - Old Bank Road, Mirfield
Sun Tan Centre - Old Bank Road, Mirfield
Old Bank Chemist - Old Bank Road, Mirfield
Maughans Bakery - Sunny Bank Road and Nad Lane, Mirfield
Shauns Butchers - Nab Lane, Mirfield
Sue Bradley Florist - Old Bank Road, Mirfield
Jane's Flower Box - Huddersfield Road, Mirfield
Airedale Heifer - Stocks Bank Road, Mirfield
The Swan - Huddersfield Road, Mirfield
The Yorkshire Puddin - Dunbottle Lane, Mirfield
Parish Cricket Club - Wellhouse Lane, Mirfield
Pizza Carino - Old Bank Road, Mirfield
Kowloon - Huddersfield Road, Mirfield
Ramsden's Butchers - Huddersfield Road, Mirfield
Maxims Chinese - Old Bank Road, Mirfield
The Shoulder of Mutton - Lee Green, Mirfield