According to vegan critics, however, this plant-based eating regimen could pose serious health risks to children.
"The evidence is robust that a vegan diet is not adequate for babies or growing children," said Nina Planck, author of "Real Food: What to Eat and Why."
Some critics express concern that parents tend to replace dairy and meat products with soy, claiming that diets largely based on soy interfere with fertility and hormonal development.
Kaala Daniel, a nutritional scientist whose book "The Whole Soy Story: The Dark Side of America's Favorite Health Food," raised these health concerns about diets with large amounts of soy.
Pro-vegan experts, on the other hand, insist that a vegan diet is very healthy, if not preferred, for children.
"I absolutely support vegan diets for young children," said Gray. She added she has seen so many parents who were so satisfied with the plant-based diet for children with kidney problems that they put their entire family on it.
Gray said she worries that general pediatricians aren't as up to speed as they need to be on this diet. "Hundreds of children are raised on soy -- if this were so horrible to all of America's babies, someone would know other than a handful of nutritionists," she said.
Both critics and supporters of veganism recommend that children who are on a vegan diet take supplements, particularly for vitamins D and B12. For parents who are just beginning the diet, unless they are well informed, experts recommend that they consult a nutritionist to make sure their supplements are adequate.
Given the excessively high protein diets many kids eat, Gray suggested that nonvegan children need nutrition consultations even more.
Yet to Daniel, fortified food and supplements aren't good enough. "No matter how well you try to do it, it's hard to get what is needed in quality form, like vitamins A and D, through fortified supplements."
In a legal context, the court might see this as "unintentional cruelty," said Daniel, who vigorously warned against vegan diets for growing children, and said parents may think they are doing best for children but could be really hurting them.
Plank added, "We need to protect babies and children from vegan diets, because they don't have a choice about what they eat."
Sasser also suggested that if this issue is about the alleged excessive control and mental health of the mother, the father's attorney might be able to argue that she is impairing the children's relationships to the father and the father's family, driven by her alleged concern for example, about the grandparent's leather furniture and nonvegan lifestyle.
"I don't think that because of one parent's vegan diet alone, the other parent deserves custody over the other," said Lanou. "Parents always have to decide what their kids can eat, and everyone else has their own opinion about the best way to feed children."
But when it comes to deciding which parent should get primary custody, the otherwise personal decision about what to feed a child could weigh in to the dispute if one parent's diet of choice is proved harmful to the child's welfare.
"We shouldn't be experimenting with this fashionable and seductive diet that the impedes growth of our children," warned Daniel.