How do I cope with being underpaid for such important work?

You help shape children during the years that matter most, and you are paid less than people who park cars. That is not just frustrating, it is a real injustice, and you are right to feel it. The world often pays the least for work that matters the most, and pretending that is fair would be a lie. Two things are true at once, and you need to hold both. First, your pay does not measure your worth or the worth of your work. The market is often blind to what is truly valuable, and childcare is proof of that. What you do echoes through those children's whole lives. Do not let a paycheck convince you otherwise. Second, you still have to live, and it is completely fair to want and pursue better pay, through a better employer, more training, credentials, or organizing with others in your field. Holding pride and practicality together is the honest path: refuse to believe you are worth what they pay you, and also do not accept less than you have to. One step: look into one concrete way to raise your income in your field this month, while reminding yourself daily that the value of your work was never up to the market to decide.