Kids can be difficult to understand, but being able to properly care for them is important, even if you don't plan on having children.
1. Be patient
The most obvious and least-possessed trait needed when taking care of children. All kids need a patient caregiver because even the most well-behaved children can act out. Children are not always good at expressing their emotions, so they throw temper tantrums instead. It's best in these situations to avoid feeding their need for attention. They throw these tantrums so you'll dote and give them attention, so deny them that and they'll calm down.
2. Have sympathy
Children have much lower pain tolerances than adults. So they cry if they get a scratch. A lot. You just have to be sympathetic towards them, and they'll reward you for your sympathy by trusting you more. Children dislike when adults are apathetic towards them, it all goes back to that attention thing again.
3. Be playful
Obviously, children will like you better if you can be playful and silly around them. It's much more fun when adults join in on their games, and you may even have fun yourself while you're playing with them. It'll be like resurrecting your inner child.
4. Be understanding
You have to understand that children will not always do what you want them to do. You're not their parents, and they don't want to listen to you. You're a stranger in their home. Just because you want them to calm down and color, they may want to run around the house screaming. It's annoying but normal.
5. You're not the parent
It is not up to you to punish other people's kids. Their parents aren't paying you to teach them to behave, they're paying you to keep them safe. If a child is acting out, you calmly tell them not to do something. Don't yell. Yelling just makes them cry, and then you have a crying, screaming child to deal with.