Nanny Needed For Primarily 1 Child In Portland, Occasionally Helping With The Child's Older Siblings

I am looking for help with my sweet and precocious toddler girl (21 months). She is a happy, amiable child, very well socialized on account of our large family. I am a stay out home mom with four children. My three older sons 10, 8 and 6 are in school most days. I would like to hire someone to help with her 2-3 days a week (usually 8am-4pm) so that I have time to run errands, work-out, complete other tasks etc. We would prefer someone who could help out with light housekeeping, and primarily focus on our toddler but is comfortable having the boys around at times. Please note that we have an elderly, small, non shedding dog.