Hello sanouette
You can make anything fun by just using a bit of creativity and imagination. By three, my children where eating mostly what I was albeit cut much smaller and minus the salt, heavy spices and chillies; I would just 'present' their food slightly differently.
For instance, using cookie cutters to cut out sandwich shapes, creating a "scene" using things like mashed potatoes as sand, steamed broccoli as trees, steamed carrot flowers (cut down the sides of the carrot to create the petals, then slice into flowers) and fish or animals made from chicken breast or ham, etc. Children have great imaginations and if you tell them this plate of food is a Pirate's Ship or a Jungle or the Seaside, they'll play along and see it.
Another fun thing is to use a muffin tin and base the food around a 'theme' such as 'Green Food' (colour recognition) or 'six pieces of...' (matching, numbers and counting) or 'Food that Starts with the Letter 'C' etc' (naming) or 'Food from a Favourite Story or Nursery Rhyme' (memory.)
Here is the site of Muffin Tin Mom who organises weekly 'Muffin Tin Mondays' and she does it with flair and creativity! https://michellesjournalcorner.blogspot.com/search/label/Muffin%20Tin%20Monday
I'm lucky that none of my children were picky eaters, why weren't they? They never got the choice to BE picky. Our rule is you take a spoonful/forkful of anything to try, and after chewing it and swallowing it and you don't like it, you don't have to eat it again. Unless you change your mind later. And, f they decided against something on one occasion, they always decided to have it again later, eventually. I believe that's empowering your child to be able to make a choice when they are young. Then it doesn't become an issue later.
I always gave my children raw veg to eat from a VERY young age, so they got the taste for it, like using frozen organic garden peas to add to hot food (such as soup) to cool it down. They could stir it in and tell me if they needed more to make the food cooler.
I always had different colours of raw bell pepper strips, carrot flower slices, satsumas, sliced unpeeled hothouse/European cucumber, cherry tomatoes, etcetera on hand in the fridge for snacks or with us if we went out for the day.
I think it's wise to remember that children (and adults!) only NEED the amount/volume of food that is between the size of their one fist or two fists together for a meal, and no more. Which seems very little from our adult viewpoint, but is just right for THEM. (One fist is the size of a normal empty stomach, two fists is the size of a normal full stomach.)
Make sure that fistful is packed full of good, nutritious stuff, no junk!
I hope that helps!
I would thinly slice a red onion and he would gnaw on that from probably 16 months, it might have been earlier, I forget (he is almost 22!) I would also give him raw grated apple in a little Tupperware covered dish to eat and and a baggie of raw red, green and yellow bell pepper strips, steamed carrot slices and raw organic garden peas. Nothing that he could bite off and choke on. Usually he would 'gum' the veggies until all the juice was gone, it felt good while he was teething. 
