Originally Posted by
hungarianhc
Thanks, everyone, for the clarity! We love exploring cities with our little ones, but we also enjoy a good beach resort. This is indeed part of a larger trip (NYC beforehand, Paris / Egypt after), and it sounds like we should just stay in Lisbon, enjoy the culture, food, and plan a couple day trips! We'll find some resort relaxation later on the trip.
Another dimension I was thinking about is the weather - your chances of rain are much higher in October so this is yet another reason to stay in the city of Lisbon and select best beach day(s) based on the weather. You could be lucky and enjoy a run of blue sky days (Sintra is also best visited in sunny conditions). Equally you could have overcast conditons for the entire duration. On average, Lisbon has 8-11 rainy days in October, versus around 3 in September. I would expect early October to have the best chance of the driest, sunniest, warmest conditions.