Just returned from Cinque Terre last September. We stayed in Vernazza. First, leave the car and take the Train. A car is useful in Tuscany but will be an albatross in Cinque Terre. Trains connect all of the villages. Taking a ferry is fun and scenic as well.

The hiking is strenuous as there is a lot of vertical so likely too much for a five year old. It took us 1.5 - 2 hours to hike from Vernazza to Corniglia. It was about 3.7 miles and was UP most of the way. I am including a photo of Vernazza, taken at the beginning of our hike, just above the city. BTW, when in Lucca, be sure and eat at La Buca Di San Antonio. Great place.

Vernazza