Definitely don't tell them. Although you want to do it and are dead set it will happen, life can change, and it's so far away, you can't say with all certainty it will happen. Job losses, relationship problems, debt, or your children's needs, parent illness or changes in circumstances, relocation etc etc etc... Not wishing gloomy things on you, but just pointing out that for better or worse, life isn't predictable and to potentially damage your employment prospects on a far off plan, well, it's not doing yourself any favours!
If they ask about the future, you could say that you'd love to continue working there (which is true), but eventually it would be amazing to be able to requalify and work for them as a nurse/ different position. I would be clear that you are enjoying and satisfied working for them and feel so lucky to be working there, and make sure they hear your future plans as a possibility in the far off future vs a definite plan and a done deal. Use phrases like 'in a few years' and 'eventually', 'potentially' or 'if possible'.
Yes that would involve lying, but I don't think your job would be safe if you don't.
You will be kissing goodbye to any sense of returned loyalty to you, they will regard you as expendable, temporary and therefore excluded from promotion, wage increases, professional development, and held at arms length in team and working culture. If you're regarded as temporary or not committed to them, then they may decide to look for your replacement sooner rather than later. Assuming you're a great employee, with passion and skill in your role, then you'd be making the school miss out on a good employee who can add a lot, as well as ruining it for yourself. Not a good thing for them or you.
And this way, they get a great employee who may be able to keep ties with them and returns to them in a different position.
By the way, I know some professions are still rooted in a more established working culture, but the world has changed.
Many (most?) sectors are no longer about the job for life, or even the job for years. There was a report released recently that predicted children growing up now may have 20+ jobs in their working lives, and in at least 4 different industries. People (bosses and employees) can no longer plan their futures over decades. People are now existing with 'foreshortened futures' where they can only plan for the next year or two at the most. Not great for stability, but great for seizing opportunities and being agile and adaptable.
Over a year is a long time now, I certainly wouldn't be able to employ people who said they'd want to stay for 5+ yrs. Whereas a few years ago, interviewees would say that even if they didn't quite believe it themselves (!). Now people, especially in their 20s will openly say they can't plan that far ahead although they're very committed to the job. This will become the norm across industries.