Spain with 2 & 4 year old: where should we go?

The kids are too young to appreciate cities such as Granada and Seville and neither would suit your idea of some relaxing down time. So what if you live near a beach, why should that preclude you from visiting a coastal town/city that you've never been to? I live on the coast, have easy access to beaches but I still enjoy visiting coastal towns around the world. Malaga or Marbella would work, Marbella being smaller and a bit quieter than the two or there's Estepona a little further west which is a charming, traditional Spanish coastal town with a mixture of nice beaches and traditional white washed buildings and attractive squares. Gibraltar will also be within close distance and the kids are bound to love the monkeys on the Rock and the caves.

Malaga and Marbella are nice, but you will find the beaches in Costa del Sol somewhat disappointing. Still, you can take in some sightseeing with kids, but need to slow it down.

I remembered this recent Barcelona with kids review. Older than yours, but did mention a park outside the usual tourist stops. https://community.ricksteves.com/travel-forum/trip-reports/barcelona-with-young-kids-d4500c90-7503-4dc2-a20f-15303b067c1d

No personal experience with kids that age in Barcelona ( or Spain).

I noticed the mention of kids and monkeys at Gibraltar. If you consider this, be very aware that the monkeys are aggressive and not kid friendly. People can be and are injured by monkeys.

I’ve witnessed the aggressive behavior both in Asia and Gibraltar. Despite quite a bit of “monkey experience” while hiking in Asia, one of the Gibraltar critters grabbed at my day pack in my hand as I walked past a troop at Gibraltar. I was watching those in front of me and another “sneak attacked” from behind. Another tourist warned me and I managed to keep the pack.

I think it depends what kind of kids you have and what kinds of parents you are. When my two oldest were 2 and 4 we walked all over Charleston, South Carolina. The youngest was in a stroller and oldest was walking. We bribed her with ice cream and stopped in the afternoon at a fountain that the kids played in (along with a lot of other children). We tried to do a modified version of what we had done before kids.

I have been to both Granada and Seville. I liked Granada better than Seville but Seville might be better for young children. Granada is far hillier and has cobblestone streets in part. I recall lots of families strolling around in Seville too.

We took the fast train from Seville to Madrid and that works really well. You don’t need a car in Seville itself. We rented an apartment but only had ourselves and our daughter who was studying in Spain for the semester. We were near the center as I recall which worked out well.

I noticed the mention of kids and monkeys at Gibraltar. If you consider this, be very aware that the monkeys are aggressive and not kid friendly. People can be and are injured by monkeys.

The monkeys, or rather Barbary Apes, in Gibraltar can be aggressive but rarely so. It all boils down to how you interract with them and also to use common sense. Whilst I allowed my kids to have the apes placed on their shoulders by a guide they were in their early teens, I certainly wouldn't do it with a 2 and 4 year old however that doesn't mean they won't enjoy watching their antics.

Our experiences were clearly different. They are wild animals and unpredictable. There were certainly no guides touching the macaques in 2019, but there were warnings about leaving them alone. If you've been recently, things have changed.

The "Barbary ape" is more properly titled the "Barbary macaque". Native to Morocco and Tunisia.

I saw more than one child frightened of the animals when I visited Gibraltar. If not "aggressive", they were certainly assertive in attempting to grab purses, food (obviously), beverage containers, my day pack, others' hand carried items. I was quite wary when having to walk past them on the stairs with no escape route. As I said, one had already attempted to grab my day pack at Gibraltar and I've had Asian macaques land on my back, spit at me, and watched others chased in Asian national parks and hiking areas.

Even in "tame" areas such as the open macaque exhibit in the Singapore Zoo there are warnings to not look directly at the animals and not to touch railings where a macaque is seated. Macaques view this as aggressive behavior - they will attempt to defend their territory.

https://naturereserve.gi/general-guideline-when-viewing-the-macaques/

We travelled with our kids at 7 and 9 and found a lot of small playgrounds in almost any historic neighborhood we walked through and stopped at many of them. In Madrid, we went to Retiro Park 2 or 3 times different days (rowing, glass pavilion, more than one playground), as well as Madrid Rio. You probably could stay in Madrid and walk through the plazas, maybe through the Royal Palace or visit the Archeology museum?

We were only briefly in Seville but it also seemed to have lots of playgrounds and, as was mentioned before, is relatively flat if you'd like to push a stroller around and explore pedestrian friendly streets or parks, like Maria Luisa. We took a horse drawn carriage ride tour as well as going to the top of the Metropol Parasol for the views.