Hello! We are planning to visit Portugal for the first time in late July for about a week. We have two small children and we love good food and coffee, small villages, shopping and generally just going for walks, seeing sites and enjoying the vibe of a new place. We will not have a car. We are thinking 3 nights in Lisbon then train to Calcais where we will spend 2 nights, day trip from there to Sintra then from Sintra back to Lisbon where we may need to spend another night before flying out. We don’t like moving around too much which is why I thought just staying in two different places. What do you think of this itinerary? Grateful for any modifications! Our youngest daughter is 3 so we will be a bit restricted in terms of long days out - too much walking etc.

Thank you in advance.

I would not recommend visiting Sintra as a day trip. For one thing, there's FAR too much to see there in a single day. For another, it can be unpleasantly crowded when all the day trippers are around. With only a week, I think you are wise to choose only two destinations. Whether that's Lisbon and Sintra or Lisbon and Cascais is up to you.

If you choose Sintra and Lisbon, note that you can take public transportation straight from Lisbon's airport to Sintra. The same may be true of Cascais, I don't know. That way, you can put all your time in Lisbon in one block.

Personally, I would want to be in Lisbon the night before my flight. YMMV.

Cascais has beaches, with children that's a plus.
From Cascais you can take the bus to Sintra, #1624 is longer route, #1623 is a shorter route.
Both start at the bus terminal across the street from Cascais station (north) and end at Portela de Sintra train station.