I am off to Mallorca next week - have been Oct half term for the past 7 years. Most years the weather has been really nice and people sit on the beach and sunbathe. My son has been swimming in November in the sea, but the pools are far too cold. I would take a swimming costume, and during the day you should be able to wear shorts and a tee shirt. The evenings are cooler than in the summer - I tend to wear linen trousers, and I would take a fleece or a cardigan. Last year was quite remarkable because it was so warm, even in the evenings, but I am not expecting to be quite so lucky this year. You may get some showers so a light small umberella or a kagool that is easy to pack might be useful.
Hope it stays fine for all of us

Keep an eye on the weather forecasts as it has been raining a lot the last couple of days. They say it will get better, but keep an eye on it anyway. When it is not raining temperatures are between 19 and 22 degrees and a bit chilly during the evening.