French after school nanny NW3

Looking for a French after school nanny for 1 or 2 days a week from 3.30 to 6.30pm for 2 girls ( 2 and 4) in Belsize Park. The girls have been in a bilingual nursery so far but will start school in September and I would like them to be able to speak French regularly. Mum is French and Dad is British.
Happy to be contacted by a nanny or a local family looking to share. We are completely flexible on the days. Available for occasional baby sittings preferred.