I agree YANBU. The issue really isn't jobs per se, or feelings per se, or the sex of the individual concerned, but about communication, mutual discussion and mutual agreement about what's best for your family going forward. Any decision which affects a family practically, emotionally and financially should certainly be discussed before any final steps are taken - not least because one person on their own can't always imagine the potential pitfalls (or, in some cases, selfishly chooses to ignore them). It's not right that anything which affects other people adversely should be presented as a fait accompli.
Yes, it sounds as though your particular household can bear the overall drop in income as a result of this but to steam ahead and arrange this without speaking to you first - i.e. prewarning you - is selfish. Unless you're impossibly well off that drop in income will have an effect somewhere down the line - even if your day to day living standards don't alter, I assume you'd have less to put into savings for example and therefore your security is compromised. I fully accept that sometimes you have to adopt a no pain, no gain approach if in the future the end result is better in some respect (e.g. potential future earnings, better CV, better mental health etc) but that's something which you should both buy into. And yes, it's a damn cheek to lump the childcare issue on you .... you may well have organised this in the past and might well have been "good at it" but how very presumptious to assume you'll sort out the issue now which he's caused without any prior consultation!
I'm afraid I can't help feel he's been selfish and would also think the same of a woman doing the same thing. I appreciate he wants this job for all sorts of reasons but when you're in a family you really do have to consider the overall effect of what you want vs what the family needs and sometimes, it's not quite so simple as fulfilling yourself is it ? Dare I say he's had a pretty easy time of it so far - not many people are fortunate enough to be able to give up a job they hate, let alone one which wasn't out and out awful - and I do think he's taken you - and I guess the children too rather for granted. In other words, I really don't think he's sat down and thought about this objectively and has instead perhaps been carried away with the excitement of a decent sounding job that he actually didn't have to (by the sounds of it) put too much effort into finding - which is a position very few people are lucky enough to find themselves in these days. I'm not sure he's thought much about the children - what does he intend to do, for example, about re-organising activities and/or dealing with upset if and when stuff is dropped ? I'm saying BTW that kids have a god given right to certain activities - but if they're disrupted without a second thought, and the reason for that disruption wasn't necessarily vital then I do think he's been selfish.
You're in a difficult position because it seems a done deal and obviously you can't demand he rejects the job. What you can do though is insist he organises childcare asap and thoroughly so the kids are placed in the most suitable care (rather than - necessarily - the 1st childminder he finds) and he must also promise that before doing anything drastic again he must speak to you so you are equally informed about what's happening and also get a chance to voice your opinion.