Does anyone know the rule for accents in Spanish?

I realise that there is controversy about the usage of accents over the capital letter at the beginning of a sentence. Sometimes people just leave them off, and they think this is acceptable, when really it is mandatory. The accents should always be used. My question is this: how come accents are sometimes left off small case letters? Example: .....y esta es my hija....y este es mi hijo. Shouldn't this be �sta es and �sta es. I have the book "Conversational Spanish in 7 days" Look at page 1.