Portugal in general is really beautiful and so so welcoming (in particular with kids!)!!
Porto is great: hot but with ocean air.
Foz was a perfect mix for our family: beaches, a quiet and nice neighborhood but pretty close to the center by bus!
Easy to park too and with unusual & old style groceries and shops!;)
The apartment was perfect (nice design, simple furniture and a useful air con) and our hosts were great! They prepared some child furniture for us and even beach toys! And a nice bottle of wine and sardines for the arrival too;)
It was simply the best holidays we had in years!!!