Hydration is more important than food at this point. Milk, water, electrolytes. Take cues from them if they want food. Their appetite will come back.
Pedialyte with water would help. Broth of some kind, any fluid is good! I hope they feel better soon🙏
As long as they’re taking fluids and passing wee then it’s quite normal for them not to eat. Obviously if it goes on for a very prolonged period then get them checked but a few days is fine. If they have a cold they could have sore throats - when my son had tonsillitis the nurse recommended yoghurt/icecream/lollies