itenerary for 10 days in Spain

Way too rushed. It seems you’ll be spending as much time traveling as visiting places. With only 10 days, possibly limit the visits to Barcelona, Madrid, Toledo, and Segovia. It’s a difficult choice since all the places you want to visit are worth visiting. I did a somewhat similar trip with my children in 1994, but we had a rental car and 3 weeks time.

This would be a punishing schedule travelling on your own, but with two young children? Sorry. Unrealistic.

Arriving in a city at 10 pm, means, assuming no delays, that it could be closer to 11pm by the time that you arrive at your accommodation.

Pick three locations that appeal. All the places you mention are worth a visit.

April means school Easter holidays, so places will be busier.

Maybe then stick just to Madrid, Toledo, Barcelona and Seville? Between Toledo and Segovia which one would you recommend? From what I read, Madrid seems to be more for museum lovers. Since we are with kids, should we plan on spending less time in Madrid?

Yes, much too much moving around. Here are some specific comments to help with your adjustments:

There are many sights in Barcelona that require pre-purchased, timed tickets. When you've worked up a list of the places you may want to see, come back here with your list so we can tell you what needs to be pre-booked. I really enjoyed the walking tour of the Barri Gotic offered by the tourist office. It's an interesting area to see, and the tour provides a bit of historical context.

Are you flying in from the US/Canada/Australia/New Zealand? If so, what with the very late arrival, I'm not sure you're going to be fully functional on Day 2.

I would not take a combined bus tour of Toledo and Segovia. Each is easily visited on your own by train (Toledo also by bus, but that takes longer), and a do-it-yourself visit would allow you to set your own pace. Toledo is extremely atmospheric and is worth a whole day by itself. Even adjusting for having young children along, I can't imagine cutting Toledo so short that you'd have time for Segovia on the same day. Segovia will of course be a big hit because of the aqueduct, but I think it need not take all day.

I don't know what to suggest in Madrid. I do not like palaces and the Palacio Real was not an exception. The art museums are great but may not appeal at all to the children. From an architecture standpoint, Madrid is just not as interesting to me as most other Spanish cities. I'm sure others will offer some suggestions.

I haven't been to Marbella, but I think you'd do best to omit it on a trip of this length.

One day in Seville (and after a super-late arrival at that) is painfully short and allows no time for Cordoba.

Lots of good choices, but I agree to think "less is more." We spent 4 nights in Madrid, day trip to Toledo, and 4 nights in Barcelona. Madrid does have a fair amount of Museums but also kid friendly.

Google Santorini Dave Madrid. He has "The 10 Best Things To Do in Madrid With Kids." He also does a great list for Barcelona. I don't think you could go wrong with a couple cities like Madrid & Barcelona.

My wife and I enjoy both Toledo and Segovia and if forced to choose, we’d pick Toledo. It has more sights to visit and streets to wander. For any trip with children it’s important to try and find things to see or do that they want to do. On our trip with our children, my daughter only wanted to swim and my son wanted to play basketball. We camped most of that trip and chose campgrounds with pools and basketball courts. In Madrid they enjoyed renting the boat in Retiro Park and rowing around. They also enjoyed the armory portion of the royal palace and the Plaza Mayor. They were bored with the Prado.

Hello, firstly, I would stick with either:
Barcelona//Madrid (and surroundings)
or
Andalucía

Secondly, I wanted to bring up that you may be traveling (depending on your dates) in Spain during Holy Week (Semana Santa) which is April 14-21. The majority of Spain's cities, towns and villages, all have their own processions and celebrations combining music, art, and color.

There may be some slowdown in those cities, towns and villages attributed to Holy Week. Note that Easter Monday is a public holiday in Spain, so the large majority of shops and restaurants will be closed. I think that you should try to make a point of seeing some of these very moving Holy Week processions.

With 10 nights I would do something along these lines (assuming you will be traveling during Semana Santa) for Barcelona//Madrid:

Fly into Barcelona
Barcelona (4 nights)
{day-trip to Dali museum

AVE high speed train to Toledo (changing trains at Madrid Atocha)
Toledo (2 nights)

AVE high speed train to Cuenca (AVE Madrid - Valencia line, getting off at the Fernando Zobel stop)
Cuenca (1 night)
-see the Semana Santa processions in Cuenca

AVE high speed train back to Madrid
Madrid (3 nights)
{day-trip to Segovia
Fly out of Madrid

Also, here are some activities in Barcelona that your children may find interesting:

Museu Maritim de Barcelona - a maritime history museum close to the Columbus statue/La Rambla. The museum is built into the former medieval dockyard of Barcelona. Tells the story of the Spanish Navy and Catalan seafaring, from the 15th century up to the present, through a collection of navigation instruments, weapons, and ship models etc. The highlight of the museum is the full-scale replica of the royal galley used by Don Juan de Austria at the 1571 Battle of Lepanto, against the Ottomans.

Museu historic de la ciudad de Barcelona - Houses the archaeological remains of Roman Barcelona (Barcino) together with the medieval royal palace, Plaça del Rei. The really cool part about this museum is that the Roman ruins are actually all underground. You take an elevator down to a 4,000 square meter subterranean archaeological site, directly below the Gothic Quarter. The adjacent Plaça del Rei is also where Christopher Columbus met with Queen Isabella on his return from his expedition to the New World.

Montjuïc Fortress - A large 17th century military fortress on top of Montjuïc hill, which over looks Barcelona. The Fortress also has a rather dark past as it was a political prison during the Spanish Civil War and subsequent Franco regime. There also used to be an extensive military museum there but it was greatly reduced in size in the mid 2000s. The highlight is more the commanding views of Barcelona rather than anything inside the fortress.

Hope this helps! :)

Drop Marbella & Madrid. Concentrate on Andalusia and Barcelona. April is a good time for both.

Day 1 - Arrive late evening in Barcelona (4)
Day 2, 3, 4 - Barcelona sight seeing
Day 5 - take morning flight to Seville (3)
Day 6 - Seville sight seeing
Day 7 - day trip to Córdoba by train
Day 8 - rent car and drive to Ronda (1)
Day 9 - drive to Granada (2) and return car
Day 10 - visit Alhambra
Day 11 - late flight to Barcelona (1)
Day 12 - take flight back home

Don't forgert Alicante & La Manga del Mar Menor! lovely places