Welcome to the site, and congratulations on choosing an excellent slogan for your school.
The second translation does not express the right idea. Cras (“tomorrow”) is an adverb, so it modifies inspirante, not principes, meaning: “Inspiring the leaders tomorrow.” But you are presumably inspring them today. It also seems random that the participle was put in the ablative case.
The first translation is correct and means “breathing into the leaders of the future,” but, yes, also “inspiring the leaders of the future.”
- Princeps for “leader” is fine if you can get over the fact that it sounds a bit like “prince” (of wich word it is in fact the progenitor). The principes are the most distinguished and influential men, the chiefs.
- Inspirare is not such a good fit. It has lots of other meanings, and to the extent that it means to inspire, the object is typically the thing that is inspired (anger, compassion, etc.) and not the person in whom it is inspired. In my opinion, this is a rather unindiomatic use of inspirare which one might want to avoid.
I am frankly not quite sure what happens to students at your school when they are inspired, but I suppose it not unfair to assume that they are given self-confidence, their creativity is awakened, they are imbued with knowledge and understanding. To encapsulate all these, I suggest the verb excolere, which means: “improve, ennoble, refine, perfect.” It can be used of people, of the mind or soul, of a way of life.
Additionally I suggest to get rid of the plain infinitive and use the first person plural (“we inspire future leaders”), which is what the slogan really means; and so we arrive at:
Futuros principes excolimus.
Note: Word order in Latin is famously free, so you can shuffle these three words around as you please. (For example, if by some lucky accident your school's initials happened to be P.E.F., it would be perfectly fine to say: Principes excolimus futuros.)