Learn Spanish (Spain): Tu hijo lee el periódico.

In Spanish, tu without an accent mark is the possessive word for "your". The version with an accent mark, tú, is the subject pronoun for "you". Since this sentence says "your son", we use the unaccented tu.

Would I say tus hijo if I am speaking to multiple people?

No, the possessive word tu only changes to tus if the thing being owned is plural (like tus hijos for "your sons"). If you are talking to a group of people in Spain about their one shared son, you would use vuestro hijo instead.

Since the sentence starts with tu, why does the verb end in "-e" (lee) instead of "-es" (lees)?

The person actually doing the action is the son (hijo), which is a "he" (third-person singular). The verb must match the person reading, not the owner. So we use lee (he reads) instead of lees (you read).

Why is there an accent mark on the "o" in periódico?

The accent mark tells you to put the spoken stress on that specific syllable (pe-ri-ó-di-co). Without it, the normal Spanish pronunciation rules would make you stress the second-to-last syllable instead.