A baby girl fed a vegan diet by her parents was so malnourished by the time she was 19 months old she didn't have any teeth and looked like she was just three months old, a Sydney court has heard.

The toddler's parents – who can't be named for legal reasons – have pleaded guilty to failing to provide for her, causing danger of serious injury.

Court documents reveal she was fed oats, potatoes, rice, tofu, bread, peanut butter and rice milk. A mouthful of fruit or two sultanas were her snacks.

The eastern suburbs couple, who hadn't vaccinated the toddler, faced a sentence hearing at Downing Centre District Court on Thursday.