We traveled to Spain with the kids and thoroughly enjoyed our trip. The weather was warm during the day and cool at night. Best way to pack would be to check the forecast before you go and pack accordingly. I picked brighter colors and prints, especially for Barcelona as it is a city inspired by Gaudi. Spain has some of the most incomparable architecture. I hope that everyone gets a chance to visit there one day.
Shoe wise I kept it simple with some adidas as we were walking miles a day. Spain was full of fun and adventure and very family friendly. I highly recommend it to everyone to visit!