What you did is called a "run on sentence". It's too long. You need to divide it into two sentences.

May I help you is the best and most polite way to approach someone. That just be your first question. Then you can ask are you lost. If your first question is "are you lost?" It can be taken offensively because you are implying that the person does not belong where they are.

The meanings are very similar but also different. So it depends on which meaning you want. "It's a typical book for children." - means it's a very popular book for children. Or that many children read it. "Its typically a book for children." - means that the book is on a child's reading level, but adults will also read it and enjoy it. I hope this helps.