Button size synchronisation

Hi,

I have two buttons, a parent and a child. Child contains variable length text and parent contains only this child button. Parent must be able to resize freely so that child's size doesn't change, but parent's size must also resize according to the child (let's say for example that child's width defined as 80% of parent's width). My problem is that when child's text length changes, the parent's width doesn't change according to defined proportional size (or at all). Any suggestions?

Thanks!

-Opa