Baby monitor for house with thick walls

[chinateacup]

We live in a v old and fairly linear house so our ( admittedly old) baby monitor doesn't work from the kids' room to ours. Does anybody know if you can buy a booster type thing like you can for broadband hubs, or can recommend a monitor with more reach?

Apologies for avoidance of correct terminology - those science GCSEs were a long time ago