How can we obtain child benefits?

Hello, me and my husband are in uk since 8 September of this year, we both working but we have a 3 years son and I need looking him and because of that we’ll receive a low income. My husband work 40/50 hours/week (6.70 per hour) and our son only have a place in a Nursery school on January. So what we need to do to obtain a child benefit / child tax credit and a work tax credit?

We rent a house (3 bedrooms because my husband have more two child’s from other woman, and bedroom is for when they come) Both of us are Portuguese. Please help us.