Colleges vary a bit on how they count languages. Most when pressed will say that it’s the year of the language that count, not the number of years in high school. A handful want to see the number of years in high school. My younger son after researching the question decided to take Latin 4 so he’d have 3 years in high school. He knew Latin would be the lowest grade on his transcript, so it was really tempting to drop it. Plenty of colleges (even ones that recommend more) will accept students who have only done two years of a language.
And BTW I don’t think the OP’s kid should switch languages - I think all the romance languages are similar in difficulty and Spanish is by far the most useful for most Americans.
Chinese grammar (and I only took a semester at a community college in Germany) seemed relatively easy, but you have no cognates, it’s a very different grammar and the tones are a very different approach to communication. We use tones too, but to ask questions and exclaim. Trying to switch to a different way was very hard on me.