No, a Schlage key cannot fit into a Kwikset lock, and vice versa. This is because Schlage and Kwikset use different keyway designs, which are the shapes of the keyholes that the keys go into. The keyway design determines the size and shape of the key that can fit into the lock.
While both Schlage and Kwikset locks are commonly used residential locks, they are not interchangeable. Attempting to use a key that does not match the lock's keyway design could potentially damage the lock and prevent it from functioning properly.
It's important to ensure that you have the correct key for your lock, and to use only keys that are designed to fit the specific lock that you have installed. If you need to have new keys made or want to replace a lock, make sure to choose a locksmith or hardware store that can provide you with keys that are designed to fit your specific lock.