I think you mean this document:
https://treaties.un.org/doc/Treaties/1990/09/19900902%2003-1...
A couple of comments on this:
1. The Convention document doesn't expressly address it, but instructs in several places that the rights enumerated exist for children 'from birth', implying they do not apply to a potential child before it's born.
2. The United States is a signatory, but did not ratify this, and is not subject to it.
I would add that rights don’t flow from documents but rather need to be built up from philosophical argument. Perhaps they’re natural, discovered, or achieved but in any case I think we have to reason towards expansive and philosophically sound rights.
I’m not arguing that children are property, but rather your own body is. When a born child leaves your body, then they can no longer infringe upon your right of self ownership. I don’t see a conflict here.
I think I remember the UN Charter on the Rights of the Child stating that (1) children are not the property of their parents and (2) parents have a responsibility for its well-being.