Child care required in N2

I have 2 children aged 5 and 8 ( in different schools). Our needs are a bit complicated but want someone who can take and pick up ( or even just pick up) one child from school once/ twice a week and stay until 6.30pm. She finishes school at 4pm in NW3. Will need car driver. Oldest daughter needs very tender loving care so we would be prepared to pay someone all day if we found the right person. Need to have qualifications or a wealth of experience. Would suit a nanny ,May suit a post-grad psychology or teaching student or experienced mum or grandma. We would like someone who can commit for at least a year but preferably longer. We can be flexible over times/ days/ pay etc our aim is to find the right person.