Co-parenting after separation can be tricky - but this blended family's situation is even more confusing than most.
And the complexities of their arrangements resulted in one mum's fury when her ex accidentally dropped the wrong child off following a custody visit.
"Sean got me and another woman, Lydia, pregnant at roughly the same time," she explained. "Our sons are only about six weeks apart in age. Lydia's son is currently just over 15 months, while mine is just under 17 months.
"Lydia and I have identical custody agreements. We both had sole custody for the entire first year, with Sean only having visitation, and when both boys were a year old, it became 50/50 custody," she continued, saying she and Lydia have their sons for the odd weeks, while Sean gets the boys for the even weeks.
"This means Sean has both boys at the same time. He pushed for this, as he wanted a week on/week off from looking after kids. He also requested this so his sons could bond," she said, although admitted she suspects "his primary motive was getting time off."
The agreement was working out for everyone involved, until recently, when he accidentally bought the wrong child home.
"Sean had both boys this last week. He brought my son back earlier today. I was on a work call and the baby was sleeping, so Sean just sort of placed the baby, carrier and all, down on the floor and left silently," she wrote.
"When the baby woke up and started crying, I got off the work call and immediately noticed that this was not my son, as my son has blue eyes, and this baby had green eyes. Taking off the baby's hat also showed dark blond hair, and not my son's light brown hair.
Although the situation was fixed quickly, it was Sean's reaction that angered her.
"Sean came back smiling, carrying my son, and says in the most condescending tone of voice 'see? He's fine. No harm done'."
But the mother disagreed and told her ex he shouldn't have both the boys at the same time if he mixed them up so easily.
However, Sean think she's being unreasonable.
"[He] says it's an easy mistake to make, and that there were times his parents brought home the wrong baby from nursery without a half sibling to excuse it," she wrote.
Sean pointed out the half-brothers would not get to bond if they were not with him at the same time and he would not be able to work overtime on his "off weeks".
The woman then asked the Reddit community if she was in the wrong, with users divided on the matter.
"Parents make mistakes, and this mistake had no one in any danger, just a bit upsetting," one person responded.
"Separating the brothers because of a mistake is cruel. If you actually think this could occur again have an adult convo about ways to avoid it," they suggested.
"I think a**hole might be a strong word for her but it does seem like a bit of an overreaction," one Redditer said.
"Having your custody schedule decided by a judge in family court is a very expensive way to throw your entire family life until your kid is 18 into the hands of an overworked stranger who might be in a sh**ty mood," another person pointed out.
"OP is contemplating a very drastic, very expensive, very uncertain approach to a problem she can prevent herself for free."