1A child; a young or underage person. Also one's son or daughter (as seen by a parent). Both 子供 and 子ども are common in modern writing.
公園で子どもたちが元気に遊んでいる。
The children are playing energetically in the park.
子供のころは毎日外で遊んでいた。
When I was a child, I played outside every day.
うちには子供が三人います。
We have three children.
子供の安全を第一に考えて行動してください。
Please act with children's safety as the top priority.
そんな子供みたいなことを言わないで。
Don't say such childish things.