In Spain, everyone needs an identity card. And children need theirs before their fifth birthday. As my son turns five next week, we took him to the comisaria (police station, for it is there where DNIs and passports are issued - on the spot). He is now the proud owner of an electronic DNI card with his photo, which he signed himself.
Foreigners no longer have cards, just a piece of paper - not valid on its own as ID, as it has no photo, so it needs to be used together with a passport. This paper, which inevitably gets battered (at least, mine has) is called, rather ambiguously, "Certificado de Registro de Ciudadano de la Union" - Certificate of Registration as a Citizen of the (European) Union. It doesn't have a fecha de caducidad (expiry date), at least. I have friends who said they lost their card DNIs, when the time came to replace them with the paper, and then carried on using them as photo ID, as noone in Spain ever checks the expiry date (or the signature on bank cards, but that's another story).
Another card which is essential for Spanish residents who wish to travel to another European country, is the European Health Insurance Card. This is issued by the Seguridad Social (Social Security), and entitles you to free public health care in 31 European countries (all EU member states, plus Switzerland, Norway, Denmark, Iceland and Liechenstien). My husband used to be a regular visitor to the Seguridad Social offices, for employment issues, child benefit etc, and on one of his many trips to the SS office, he decided that he might as well get his Tarjeta Sanitaria Europea (TSE) while he was there. Having remarked on the speed and ease with which his card had been issued, so he got one for each of us (now you have to apply online and it's sent to your home).
But did we remember to take them with us when we went on holiday to Portugal last week? Did we hell. I'm ashamed to admit, I don't even know where they are. (Anyway, it's my husband's fault, as he's the one who applied for them. That's my excuse etc etc.) My daughter had a small accident while we were in the Algarve which needed medical attention, and the treatment was quick and efficient, but at a cost of 60 euros. And all because we didn't have our cards encima. Plonkers. Next time we travel outside Spain, it's passports and TSEs - if I can find the damn things. Have you got yours?