I'm very glad that you decided to cut out Portugal from your plan. To finalize your itinerary, here are my suggestions:
Do the math for time in terms of nights, not days.
Count 2 nights for each day of sightseeing. For each day trip, add one night.
Add the extra nights to Barcelona, Sevilla and Madrid. Keep the 2 nights minimum for Valencia and Granada.
Day trip from Barcelona: Figueres
Day trips from Sevilla: Cordoba or Jerez de la Frontera
Your daughter would love the dancing horses of the Royal Andalusian School of Equestrian Art, in Jerez de la Frontera. It's just a little over an hour by train from Sevilla. The shows are scheduled for Tuesdays and Thursdays in April, with an additional show on Easter Saturday. You must buy your tickets well in advance! So it would be worthwhile to plan accordingly, if this interests you.
Towns like Granada, Sevilla, Cordoba, etc. have little tourist trains that take you around - your daughter would enjoy these. Sevilla has horse-drawn carriages. Barcelona and Madrid have HOHO buses. Finally, Barcelona and Valencia have a zoo and, as you know, Valencia has the biggest aquarium in Europe.
Finally, do take into account the fact that Easter might complicate your plans a bit - busy trains & buses, booked accommodations, maybe even some closures. Research the opening dates & times for all the attractions that you would like to visit. Even in normal times, attractions may not be open 7 days a week...