Your kids are young.
But its good they start to, learn about food/planning/prepping/cooking.
At 3 my son could make his own scrambled eggs, for example.
And my daughter who is older, knew how to cook.
And they both, knew about how to go about making a grocery list in order to get the ingredients for what we want to eat/cook. And how to look at recipes and weed through it.
But, I did not let them solely decide, what to eat or cook.
I do. Especially when they were younger. My kids are now 7 and 10. And although I ask them for ideas on what to cook/eat, (when I am out of ideas), I decide what the menu will be and because I know what foods/items we have in the kitchen cabinets and freezer and fridge. That way we don't waste, food. Which I also taught my kids about.
So based on that, and/or what we need, I make a menu. For the week. And my kids give their input. But in the end, I decide what to cook.
Sure, my kids "help." But I don't give them carte blanche about it all nor what to cook. I gauge it. And I decide. And if... they want to eat the same thing every night, I simply say no. And if they want junk to eat, I say no. But we don't have junk in the house anyway. We cook according to what we have in the house and what we typically buy.
I don't let my kids pick from a list nor decide on the meal.
I, decide what to cook, but will ask them for ideas when I am out of ideas.
Then, based on what I will be cooking, they may help. And they know their way in the kitchen and how to cook anyway.
So the bottom line with me is: I decide what to cook and the grocery list. But I ask their input. And I don't just let my kids tell me... what to cook. I cook what I cook and they help me with prepping or cooking it.
But I personally, do not expect nor make... my kids, make it on their own. Because, I cook from scratch and there is no way, my kids, even if they know how to cook, can make an entire dinner with all the entrees and sides, on their own. Even if they are 7 and 10. It takes me... at least 1-2 hour in the kitchen, to make dinner. If my kids were to make it all on their own... it would take them LONGER. Much longer. And along with cooking/making/prepping dinner, for us, it also includes... washing the dishes along the way and cleaning up as you go and after cooking. It is a long process.
My point in teaching my kids about the kitchen... is so that they learn how to cook (which they do), how to plan meals, how to budget, how to clean up as you go and after, and how to make things healthy. And quite frankly, most of the time, I rather do it myself... because with the kids in the kitchen it just takes longer. And then I just have them prep or make the salads or watch the stove as I chop another thing up etc., or set the table.
If I were you, being your kids are so young... I would not... let them pick a meal nor plan the meals, nor would I give them carte blanche over the whole dinner decision.
For me, I do the dinner. And then my kids just help me with what I have planned for dinner. And yes, we get lots of variation and healthy variation.
By the time my daughter was 8, she was a real able cook already. And she had even made a full dinner with sides and well balanced things. She'd make a list of what she needs. And organized it all. She was making crepes too. And I just let her have the kitchen to herself. And she'd clean up after too.