Legal analysis: If the separation agreement only involves the parents' property, then it only needs the parents' signature, because it is equivalent to the gift of property, and it doesn't matter whether the children sign it or not.

Secondly, if the property of the other child is involved, it must be signed by the other party, otherwise it will be invalid.

Legal basis: Article 143 of the Civil Law of People's Republic of China (PRC) A civil juristic act that meets the following conditions is valid:

(1) The actor has corresponding capacity for civil conduct;

(2) the meaning is true;

(three) does not violate the mandatory provisions of laws and administrative regulations, and does not violate public order and good customs.