All three images show the family wearing co-ordinated red chequered shirts and blue jeans as they pose at what looks like a farm.
In one image, the woman and her husband each hold one of their biological children, with the man's son from a previous relationship standing in front of them.
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The two other images, also taken outdoors, show the woman sitting on a blanket with her two children on her lap, while her stepson sits to the right of them, half a metre away.
A screenshot of the woman's post was shared on Reddit two days ago with the user blurring out the children's faces.
While it doesn't include the original Facebook comments, the mother's "edit" suggests many were negative.
"I love my stepson but I do want some without him in them," she wrote, amending the post.
"I already posted these ones but I just want to have it both ways."
The post was then shared on Reddit and has since attracted more than 2000 comments with users expressing their shock over her request.
"It's a child! What has he done to her?" one person wrote.
"This is absolutely deplorable," said another.
"Parents seem to forget that when they get old — they'll need people to take care of them again. At least you won't have that burden," a third commented.
One woman said that as a stepmother, the request "broke her heart".
"It is my job to make sure my stepdaughter knows she is loved as much as I love my son," she wrote.
Another stepmother also expressed her disappointment, saying that while it can sometimes be "awkward", she always tries her best to make it less so.
"Whenever we did family photos we made sure to do a bunch of combos and individual pictures to avoid any hurt feelings," the mother wrote.
"We also had two extra kids that lived with us on and off for about six years. So we would do all the kids, just girls, just boys, oldest with youngest, middles, me with all boys, all girls, all kids, husband doing the same."
While the woman said she always thought she would want the pictures with just "her" kids, the photos with all the children were her favourites.
"They were also the most honest and true. Nothing like five goofy kids ages 1-16 and big smiles to make a wall look good," she wrote.
Others went on to say how heartbroken they were by the mother's request to crop out her stepson.