Otherwise you ate basically saying his job, and therefore employer and clients, is more important than your job and your employer (school) and clients (children).
I disagree. It's saying that family is more important than a job, and I should imagine that the vast majority of people feel their family is more important than their job. That doesn't mean they see their job as unimportant though.
TAs are not particularly valued by their employers. They might be highly valued by their colleagues and even the head of their school, but the local council and government don't value them, they know they could replace then at the drop of a hat. So why should TAs and other school support staff be expected to turn up at work in genuine circumstances where their child is sick when it will be detrimental to their family's finances?
If school support staff are that important, and I wholeheartedly believe they are, then they should be paid accordingly and there would be unlikely to be such a difference between their wage packet and that of their husbands.
Families do have to prioritise the main breadwinners job over the job that provides the supplementary income. I love my job and I'd probably do it for free if I won the euro millions, but like most people, I do it for the money and my family is more important. If it's a choice between losing a day of my pay or my husbands pay, then we will choose to lose mine simply because it's less than half that of my husbands. It is very much not because I think my husbands clients are more important than the children I work with!