I would just keep offering, in my experience they eventually eat some. If dinner does not get eaten, nothing else is offered.
If they are eating well during the day they will be fine without dinner, if they are truly hungry they will eat what is offered. I know it is hard to resist giving them something like toast but i have found this only makes it harder as it is easier to refuse food when you know you will get something else if you do.
I also find involving them helps, i started a veggie patch and my girls really enjoyed helping me plant/water the seeds and then eating what grew. I also involve them dinner making and give them a variety of things to try.
Good luck, i know it very frustrating.