How do I teach my children not to criticise food and to appreciate blessings at home?

The Prophet ﷺ never criticised food; if he liked it he ate it, and if not he left it without disparaging it. Teach your children that running down food hurts the person who cooked it and lessens gratitude. Encourage them to say something good about the meal, or stay quiet if they do not like it much. Set the example by not grumbling about the cooking at the table. Explain that food is a blessing many people do not have. Start by praising the effort of whoever cooked every time you eat together. See everyday adab.