Bit of a blanket statement there.
Children come first. But not at the expense of everyones mental health.
Adults need a break sometimes. Adults need some downtime. We all have needs but for the most part, these can wait until an infant's needs have been addressed.
Babies needs supersede anyone else's needs. They can't do anything themselves. They are a priority.
As children get older they can start doing some things for themselves and learn that not everything can be addressed instantly.
It is important everyones needs are looked after; everyone is well mentally and physically.
For instance, I like to do my nails for a bit of self care. Or my eyebrows. I can't do it whilst my toddler runs around. I have to wait until he's in bed or OH looks after him.
In the early days, DS's breastfeed came before my own needs of food. I would wait until he was feeding or asleep and OH would go and get me a sandwich as I was stuck wherever I was then.