I know that it is a commonplace in popular culture that children supposedly don't like spinach, but I have to say, I don't buy it. I always liked spinach, in fact I adore it, not only due to Popeye the Sailor.
My hypothesis is that if you don't like spinach, you've probably only tried it in a badly prepared way. There is one very important rule: don't overcook it. Wateriness is the enemy of spinach! Apart from that, there are many viable methods to prepare it. Young leaves don't even have to be cooked at all, they make an excellent base for a hearty salad.
When you buy spinach, check that the leaves look bright and fresh. They should crunch and squeak as you stuff them into your bag or basket. Plan about 250g of fresh spinach per person. The sheer volume can be intimidating, but it looses most of it, so don't be afraid to buy too much! The fastest way to prepare spinach is to blanch it. Boil salted water in a large pot, throw in some spinach leaves, give them a stir and let them cook for only 15 to 20 seconds. Take them out, shock in cold water and drain - done. Press out the excess moisture a bit, the leaves can be used for decoration, or added to other dishes, for example an omelet.
To make more of a dish on it's own, cook spinach thoroughly, but don't use any water at all! Just clean it and stuff all the wet leaves into a large pan, put on a lid and bring it to low or medium heat. Don't worry if the lid doesn't close, just press it down a bit. The spinach will quickly loose volume and stew in its own juice. After five minutes or so stir the spinach and turn up the heat a bit. When it's done, drain excess fluids, and add a chunk of butter. The spinach will absorb all the butter, it's almost like a natural symbiosis. Season with salt, pepper and a bit of nutmeg.
Or why not just bake it? Oil a baking tray and rub in a single clove of garlic. Lay out the washed and dried spinach on the tray and press it down a bit. Sprinkle with some pine nuts, a bit of mozzarella and some grated Parmesan. Season with salt and pepper and bake at 220° for 15 to 20 minutes. It's a wonderful meal to share, best with some fresh bread. And remember, friends always tell friends when they have some spinach stuck between their teeth.