Yes, but in portuguese, if you have many girls and just one boy in a group, you have to call that group as if there were only boys. For example: if you have 3 daughters and 1 son, you have to call them "filhos". I think Mick was refering to this rule.
I think that the best answer is "our sibling have a cat" if we want to say a boy and a girl". "Children" is crianças generally.
Nossos filhos não são ELES? Deveria ser usado o HAs E não o HAVE.
Pkease Help me