The traditional school nativity play is under pressure to modernise the story and remove religious figures, according to users of a parenting website.
Parents on Netmums have given examples of characters such as spacemen, Elvis Presley and footballers being introduced to the nativity story.
There are also claims Christmas plays are being called "winter celebrations".
Netmums co-founder Siobhan Freegard said parents were concerned Christmas traditions were being "pushed aside".
Don Horrocks of the Evangelical Alliance, representing evangelical Christians, warned that it was either "extreme political correctness or perhaps it reflects a nation too embarrassed to face up to its Christian heritage".
"Perhaps it's a sign of collective guilt amidst national commercial frenzy? Whatever the motive, it does a huge disservice not least to the younger generation who are being misled regarding their spiritual heritage," said Dr Horrocks.
About 2,000 parents have shared their experiences of how nativity plays are being adapted in some schools - and how there has been no nativity play at all in other schools.
They report how the story has been changed, so that rather than simply casting Mary, Joseph, shepherds, wise men and a donkey, there are parts for aliens, punk fairies, Elvis Presley, footballers, a lobster and a drunken spaceman.
Christmas carols have been replaced with Christmas-themed pop songs, report some of the parents.
There were also reports of schools changing the name of "Christmas" plays, with the suggestion that it was to avoid a specific reference to the Christian festival.
This straw poll of parental attitudes also found complaints about schools charging to see a nativity play or Christmas show.
There were also schools that banned the use of photography and others where parents could take pictures but had to sign a promise not to share the pictures on social media.
Ms Freegard said that many of the parents wanted schools to keep a traditional version of the nativity play.
"This study shows many parents who aren't religious look to the nativity as a comforting part of the Christmas celebrations and want their school to embrace and celebrate it, rather than make up a version with perhaps less resonance for kids," says Ms Freegard.
"It seems wrong to bombard kids with commercial messages about presents and Santa without them realising the true meaning of the celebration.
"While the UK is a diverse and multicultural society and it's right children learn about all religions and cultures, many parents feel the traditional nativity is being pushed aside."