Depending on the child's age, there's many reasons why they might refuse to eat or drink. With toddlers starting around age 1, we see them go through kind of a picky phase and they start to eat like little birds. This is normal and during this time, they're normal weight gain tends to slow down too. So even though it seems like they're not eating enough, really they're probably getting just the right amount for their little bodies.
I always encourage parents during this time not to force the child to eat because it can make meal time seem like more of a punishment. Instead, you want to just continue to offer healthy meals and snacks throughout the day and then when they're hungry, they will eat.
Also, kids tend to get very easily distracted. They don't want to take time out of their playtime to sit down and then eat a meal, so to help with this, you can remove things like the TV and toys from around the table. Have a set meal schedule and a designated eating area and then when they don't have that distraction, they will be able to eat.
It's also important to not fill up on snacks throughout the day and kind of watch how much juice and milk they're drinking 'cause this can decrease how much they want to eat.
Then with teenagers, it is a little bit different. We start to worry about things like negative body image, peer pressure, depression and eating disorders. If you do see these symptoms, you want to address it right away.
Illness is another thing that can cause kids to not want to eat or drink. In this, especially in the toddler age group, we do see that. As they start to feel better, you will see they're appetite's pick back up again. But you do want to monitor for things like dehydration.