A million things to consider... like:
Do you need residency visas to live in Portugal?
If so, can you fulfill all the portuguese government requirements to apply for residency visas for you and your family?
Have you checked how portuguese taxes will affect your income when you live in Portugal?
Do you know that you'll have to continue paying taxes in the US even when you live outside the US if you are a US citizen? (It's the only country in the world that does that)
Are you aware that it is very difficult to find rental accommodation in Portugal, most rentals are low quality housing, and the best areas & housing are very expensive?
Areas to consider:
If you base yourselves in the center of Portugal, no furher than 1 to 1:30 hours drive from Lisbon, you'll be able to explore the center, Lisbon and both north & south. There are no places specifically built for young families in Portugal, state education starts with pre-school and is free, all through including uni.
The interior is very rural with a slow pace of life and usually services are better: free pre-school, less children per class in primary & secondary education, more attention to each individual, some rural municipalities give away an annual bonuses to each child on top of the social services & benefits available to families on low incomes.
Some municipalities in the interior offer low cost rentals to attract families to settle there, but these are usually very isolated places.