Safety during Carnival

What city specifically? The language will not be a significant barrier. The biggest risk, as in any crowd, is pickpockets.

The biggest risk will be the potential for losing your unfounded anxieties about celebrations in Spain.

A friend of mine a few years ago objected to me that it is perfectly sensible for him to worry about safety in a situation so different from what he was brought up in. "Who knows what might happen?" I looked around us and nodded at the young parents pushing their tots in strollers and the knots of friends laughing together and the foot patrol officers in their hi-vis vests smiling ear to ear, and said to my friend, "Don't you think the parents care about their babies, and so on? Aren't they like you and me? Would they be here if it worried them so much?"

If you're going to some spot infamous for pickpocketing, just don't carry anything that you don't need. Act like you're going to the gym and leave your stuff in your locker/room.

Festivities in Spain are perfectly safe, very family-oriented and with lots of activities for all ages. Carnival time is just great, you´ll see lots of families and friends in the streets just enjoying themselves...and if on a weekend, kids in the streets well past midnight. Crowds in Spain does not mean "unsafe", it means lots of families around.

Of course, things happen, but I wouldn´t consider any festivals in Spain a source of discomfort for families with kids, just the opposite. My kids return home around 6-7am during any of the many summer festivities and it´s perfectly normal, both your son and your niece will have a great time during Carnival...just make sure you can get them a costume to mix in the atmosphere of the town you´ll be visiting.

Use your normal crowded place safety guidelines, and you will be fine. I guess first, do not expect the big tourist spectacle of Venice, or the party hearty attitude of Rio or New Orleans. The Canary Island might be the closest big celebration, but Carnival is much more regional in the way it is celebrated all over Spain. I would start by figuring out where you will be, and see what they do. In many places, you might find the public celebration is limited, and the revelry is more private galas and parties.

Thanks, everyone!

I was looking at Cádiz as a possible option for Carnival celebrations, but am still very early in my reading about best cities.

We have no concerns about day time safety, we just weren't sure if it got out of control in the evening/early morning hours (like things sometimes do in the US)

The carnival in Cádiz is really fun. But there're hundreds of different carnivals in Spain, so you shouldn't go wrong anywhere.

The Cadiz carnival is almost unique. There are male voice choirs, costumed a d singing their own satirical songs, often in dialect. Many are on trailers towed through the narrow streets. There are also informal performances everywhere. It is an absolute hoot. So worth a trip. Check the dates carefully, as the singing is on specific days.