New bird in our garden

Hi I'm new and have a question on behalf of my 7 year old daughter who has recently become interested in the birds in our garden after buying a Garden Birds logbook.

We seem to have a new bird in our garden and we thought it was a young female blackbird but it seems to have a speckly chest like the thrushes that come in our garden. We've been googling for ages and are getting a bit frustrated now....can anybody help us please?

life's what you make it