Run of the mill is sort of the cornerstone of the Destin food scene. That said, for kids, Lulu's is a good spot. It's on the Bayside north of the Commons and has a little beach with cornhole and stuff and there's usually live music in the evenings. Overpriced standard fare, but like most places in Destin, you're paying for atmosphere.
Boshamp's on the Harbor has kind of a similar setup with the beach area, but better food.
Tommy Bahama is a little more upscale, but the food is very good and there is a little grassy lawn and water feature adjacent where there is frequently kids running around playing while parents continue to eat and/or have a cocktail on the patio. It's in the Grand Boulevard shopping center just past Sandestin. Emeril has a new restaurant in the same center, but we haven't been yet.
Everybody knows about it, but McGuire's is still in my top 3 in the area and kids usually get a kick out of all the dollar bills. Marina Cafe and Lagniappe are the other two, but neither is especially kid-friendly. Consistently tasty food and while it isn't cheap, the portions are very healthy.
Then of course there's fun stuff for kids at the Harbor and Baytowne, but most all those restaurants (Brotulla's, Harry T's, Jackacuda's, Poppy's, Hammerheads, etc.) are basically what I call "tourist food"...just overpriced basic seafood with smallish portions and little-to-no care or creativity put into the dishes.
Side note: word is that the June grass and yellow flies (biting flies) have already been really bad. We've also had a ton of rain recently, so the outgoing tide is going to murk up everything near the Pass pretty good. Regardless, hope y'all have a great trip!