"Our children have a cat."
Translation:Nuestros hijos tienen un gato.
Here is what I think.
You can, but its better to understand to use niños here; because 1.) It is the direct translation
2.) The use in context can change alot.
3.) Not forming bad habits, accidentally calling someone elses children your own.
Mi hija es una niña. - My daughter is a child. Mi niño es un hombre. - My boy is a man. Can sound silly As well as talking about children who are part of your group but are not your desendants. So Ellos son mi niños, pero es mi hijo. Those are my children, but he is my son. To differentiate the two.