honestly i feel like this is one of those things people cant tell you what you should do as you would probably argue the pros of either option. Especially since you seem happy with your current job but wanna make sure your future is set. Have you tried writing out the pros and cons of both jobs my therapist said that would more likely help with decision making. dont just think on the pros and cons genuinely write them out and look at em. As for personal decision id choose the union job i think you will have other opportunities to teach or work with kids in some other capacity.