Kids can easily turn anything into a mess.
Toasted sandwiches if they build them and you cook them.

At 6 and 8 they could try making sandwiches. I guess it depends a little on whether they have the skills for a sharp knife as to whether they can slice things for salads; and maybe blend things for smoothies would be safe, but could get messy!

Depends on the age, cupcakes muffins, snack plates, cheese and crackers, scrolls

What type of recipes are you looking for (dinner, lunch or snacks) ? what age (baby, toddler, school age kids) ? and do you want to involve them in the cooking or baking process ?
Since you ask mess free recipes I assume you mean for baby / toddlers in which case I suggest finger foods like potato wedges, cheese sticks, small sausages, broccoli strunks, slices of cucumber, mini tomato, cut up fruits, nuts

No bake slices are great for kids to make – and making them help clean up the mess they make as they go is a good lesson for life.

There isn’t any I know that have no mess but minimal mess I’d say cookies, cupcakes or honey jumbles (cornflakes, honey, butter and sugar) put ingredients into bowls measuring cups and get them to tip them in and help mix also as someone below said mini pizzas are good too my daughter loves to sprinkle the stuff on and isn’t to messy

What ages they are will decide what you can let the kids do something’s on their own. I think Macaroni Cheese would be good one for them.

My kids love to make mini pizza and scrolls.

I don’t think there’s such a thing as ‘mess less’ but cookies are always a good place to start. Chocolate chip or even ANZAC are simple and kids enjoy rolling the biscuit shapes.

I remember when I was first allowed to cook it was a Betty Crocker box of blueberry cupcakes.
My mum put all the ingredients like the milk and butter into separate bowls and I just tipped them into the big bowl which had the main mix in it and stirred it all together.

The premade cookie dough rolls, I think its called Aunt Kaths. My 2.5 year olds loved rolling it out and using cookie cutters

Make biscuits they are easier like Anzac biscuits or the non cooking ones that you just put in the fridge.

Quick answer….no. I can’t even cook without making a mess, how can you expect kids to cook mess free

You can’t really go to wrong with recipes such as chocolate crackles or bliss balls. I’ve tried both with children and the mess is very manageable.

It’s hard to be non-messy if kids are cooking with you. We’ve had some success with making packet mixes like cakes, cookies and brownies. Miss 6 likes making pancake shake mixes. We’ve made Weetbix balls and marshmallow rice crispy squares. We have a bread maker, and Miss 6 enjoyed helping to make a loaf.