La Sagrada Familia with a 4 year old boy

Not sure about entering with a stroller to the basilica main floor -you need to check the website- but certainly you will NOT be able to take the stroller up the spires (yeah, lots of people mistakenly call them "towers", but they're spires). This is a video of the stairs descending one of them, LOL!: https://www.youtube.com/watch?v=J143QCXhhx4 -the other one is similar.

Even without ascending the spires, a visit to Sagrada Família is still well worth: https://www.youtube.com/watch?v=Zog4rk8kt8k

For info: ascending the spires in the Sagrada Família is done by elevator, but the descent is done on foot. As you can see in the video, they're narrow so, as per safety regulations, people with severe disabilities, wheelchairs, parents with very young children, strollers, etc. won't be allowed to ascend. Should there be an emergency (ie. a fire), it'd be too dangerous for them and for the rest of the visitors (ie. blocking the descent).

Strollers are allowed in most areas but not in the towers.

See 'Rules and Etiquette - Can I bring my children and what should I know' here https://sagrada.barcelona/faq

Thank you both regarding the strollers. I have osteoarthritis so I probably won't be up for going to the spires anyways so with that not being an option, it sounds like taking the stroller will not be much of an issue as it is allowed and the main floor is pretty minimal stairs. Thank you again!

Please double check with the actual official site: https://sagradafamilia.org/en/home

The site mentioned above (https://sagrada.barcelona/) is NOT the official site, just a reseller, so the information there MIGHT NOT be accurate or up to date. I am sure @Windyram cited it with the best of intentions, though.

Furthermore, this site doesn’t look very trustworthy, as it clearly doesn't comply with current Spanish law requiring websites, especially those selling something, to identify who’s behind them. In Spain, this isn’t optional and aims to provide legal protection to customers. BE AWARE!

Under the Spanish E-Commerce Law [LSSI-CE. Ley 34/2002, de Servicios de la Sociedad de la Información y de Comercio Electrónico, Article 10]: "Any site with economic activity must clearly and permanently display who owns it, where they’re based, and their legal or tax ID nbr. Consumer protection laws reinforce this when goods or services are sold, and data protection rules also require identifying the legal entity responsible".

Nowhere on the website, not even in the "Terms and Conditions", does it say who they are, where they’re based, or provide any tax or company ID number. If they fail to provide the service you purchase (or if they're a scam) you'll have no protection whatsoever.

We did the english language tour in November. It was well done for adults but it was over an hour. As far as leaving, I do not see any issues as many people are visiting without the tour. Personally I’d skip the tour with a 4 year old and just walk through. One thing to prepare for is it is pretty crowded. On a side note, Park Guell was pretty cool, like walking through a live candy land game. I’d think your child may enjoy.

Interesting how things can vary by the day. We went to Sagrada Familia on our own at the first ticketed time-slot. It was wide open and easy to wander and see everything unimpeded. Conversely, our afternoon visit to Parc Guell was uncomfortably crowded. Good luck!