"Kid" is another word for "Child." __'s and "is" are interchangeable. For example: He's going-He is going; The book's over there-The book is over there
No. "在" means "is in". "是" and "is" are technically not the same. "是" means "is" as in "it is a cat" and not as in "it is happy" or "it is going". Btw "在" can also mean one of the other kind of "is" as in "it is going" or "it is eating" (not as in "it is happy" though).