Maybe have them help you make the food? My son is big on smell so he likes to smell things and thinks about it before just trying something right away. It can take a while for him to come around but slowly he comes around to trying new things.

also can try to put things together. Like add an egg to muffins or fresh fruit or veggies.
Also try mix meats.

Sauces and dips choices and only little amount of new food but also let them play with their food, helps Sometimes alot of meat or finger food or bite size food displayed