You're in the middle of the suck right now. Even when you want all of the things that you have -- decent job that doesn't bore or kill you, lovely kids, wonderful wife -- the reality is that each of those things places a lot of demands on your time and attention, and put them all together, with no end in sight, and you can feel trapped and itchy and bored. Even when you know you're on the right path, that path is a long one, and it requires maturity and continuous good choices, which again, can make it feel like a never-ending slog.
IME, there are two things you can do that can help your mindset.
The first one is to drop all of the "shoulds" from your life to free up time for things that are more meaningful to you. Life tends to fill up with stuff that other people want/expect from you that are neither necessary nor particularly enjoyable. Stop doing things just because everyone does them, or they're expected, or you think you should because XYZ. This tends to be particularly problematic with kids, because there are just so many expectations. But you know what? I managed to raise two kids without once attending a PTA meeting or volunteering to be a "room mom" at school or "helping" them sell stuff for fundraisers or anything like that. Your kids are probably young enough that you're not into all of that yet (and expectations in NZ may well be different), but the principle applies everywhere -- we also, for example, gave up on having flowers and pretty stuff in the yard and focused instead on just whacking the weeds when they get too high, because neither of us cared one whit about pretty gardening stuff.
Second, recognize that everything in your life is a choice, and if what you are doing isn't working any more, you have every ability to make a different choice. There are two keys to this: (1) acknowledge all of the available choices; and (2) focus on real choices, not magical ones, and consider the real-life downsides of each.
On (1): you have many, many more choices than you think; you've just already decided that some of them are off the table. For example, you could leave your family and go live as a single guy again, spend all of your spare time on your own hobbies and interests. Of course you're not going to do that! But: why is that? It's because you value your wife and kids far more than the freedom that you would have on your own. So you have already decided that it is worth giving up your free time and money to have your family, even with the additional stresses and time constraints they bring with them. Or you could quit your job and go live in a van, working scut jobs as you need to pay for basic expenses. You're not going to do that, because you value supporting your family, you value the security of having savings in the bank, you like having the house you live in and decent, reliable cars, etc. etc. The point is that all of these things are choices, and the reason you are where you are now is because you have made choices that are entirely aligned with your values and goals. Sometimes it's really good to remind yourself of that; instead of resenting all the time you spend at work, you can instead reframe that as a choice you have made to provide for your family.
And that brings me to (2): make sure that the various options you lay out are real ones. "Winning the lottery" is not an option, because that's magical thinking and finger-crossing, not something that you can control. OTOH, "find a different job that [pays more/gives more free time/provides more opportunity for growth/etc.]" is a valid choice that you can consider. Maybe you want to make more money to speed up FIRE. OK. So you can look for a higher-paying job. Of course, that will probably come with its own downsides -- more hours, longer commute, maybe requiring more schooling/training, etc. Once you lay that all out, you can decide whether the tradeoffs are worth the additional money.
So why do all of this? Because it is a reminder that you have the power here, and if you don't like where you are, you can change it. The problem with feeling bored/stuck is that it paints you as the victim; you are just stuck in this situation and can't do anything else but slog through. And that is 100% not true. You have put yourself in this situation due to your own choices, and if those choices are no longer working for you, then you have both the power and the responsibility to make different ones.
Here's the real key: you will very likely figure out that those big choices you have made -- staying married to your wife, being there for your kids, working your current job, keeping the house, etc. -- are all the best of the available choices. There is real value in reminding yourself that you chose this and remembering why; it's giving yourself credit for living aligned with your values. FWIW, I do this every time I get bored/antsy -- what is missing? what would I need to do to get whatever it is I think I want? Are those tradeoffs worth it? That process anchors me in reality (getting my head out of the lottery clouds) and reminds me why I chose what I did.
If the big pieces of your life are still working for you, you can do a similar analysis on the little choices. If life is just too much of the same thing, brainstorm ways to shake up the routine -- get a babysitter on a Tuesday night and go have a drink with your wife, or go for a family picnic instead of settling in front of the TV, or do something other than a family camping trip for vacation, or take multiple long weekends instead of one bigger trip, or try to learn a new recipe from some kind of cuisine you love but don't know how to make, or take an art class just because you know you'll be bad at it, or find some charity/community group that does things you value and offer your time to them, etc. etc. etc. The options are limited only by your imagination.
FWIW: it doesn't matter whether you thought your grandmother's life was small and unimpressive. What matters is what she thought about her life. My Granny passed a couple of years ago at around the same age. She never held a job outside the house, spent her life raising her kids and grandkids. But oh boy did she have a huge impact on her family. I'm still not sure how she did it, but she absolutely doted on us, and yet we all also knew you didn't mess with Granny -- even though to this day I cannot remember her ever raising her voice. When I'd get upset with my kids, I'd think "what would Granny do??" She had significantly fewer options than any of us did, but she made the best choices she could, and she lived a life that brought her meaning and happiness, and in the process made a huge impact on the people around her. I'm pretty sure she'd have chosen that above any kind of high-power, high-status corporate position.
