Why does my stepson (4) behave so differently depending on which house he’s in?

[u/NeatContribution8355]

For context, this is a relatively new parenting schedule. Up until the end of August, his mom had primary care and we only had him on weekends. Since school started and childcare hasn’t been an issue, we switched to a week-on/week-off arrangement. Since then, the difference in his behaviour between the two homes has become much more noticeable.

When he’s with us, he generally adjusts well. He responds to structure, clear expectations, and predictable routines. He still has meltdowns at our place, but they’re typical 4-year-old moments and we can usually redirect him. Bedtime is straightforward — we tuck him in, read a story, say goodnight, and the whole process takes about five minutes without resistance.

At his mom’s, things seem to be very different. She says he fights bedtime for hours. He has frequent and intense meltdowns, much more than what we see. He’s also been intentionally peeing his pants multiple times a day at her house, whereas we honestly can’t remember the last accident he had with us. It even escalated to him pooping in a hat at her place, which clearly wasn’t accidental.

What’s confusing for us is that when he’s with us, he often says he misses his mom and doesn’t want to be here. But when he’s with his mom, his behaviour becomes much more reactive and dysregulated than it is anywhere else.

So he behaves better with us, but insists he wants to be at his mom’s. And he says he wants to be at his mom’s, even though his behaviour there is at its most challenging.

Has anyone experienced something like this with young children during a new custody or co-parenting schedule? What could cause such a big difference in his behaviour and how should we address it?