Babysitter for one child, 6 years old, Hammersmith and Fulham

I am looking for a Babysitter for one child 2 years old. The services I need are Babysitting, Play & learn a language, Cooking/Meal preparation. We are looking for someone to come in on Saturday mornings. We would start with once or twice a month to see how things go and perhaps establish a more regular routine. What is crucial for us is to find someone we can feel is going to be trustworthy and engaging enough for us to leave our little boy with and who ideally we would build a longer term relationship with.