The update was completed this morning. You may experience warnings about "Only Secure Content is Displayed" or other similar issues about an insecure connection. This is not an actual problem, as car-seat.org is now secure and the server has no issues with privacy or security. This warning is caused because some content (like images hosted on photo sharing services and inserted with the IMG feature) is served by a third party website and may not yet be served via encrypted secure methods. Some browsers may block 3rd party hosted unencrypted images altogether. This is NOT a privacy or security concern and should be resolved over time. Until then, you may choose to display or not to display non-secure content. Either way is safe, but that content will not be encrypted, usually images sent from a photo sharing website.
Technically, car-seat.org doesn't need this level of encryption or security at all, since it's not a banking website and does not have any shopping or financial information transmitted. Even so, it is the trend and Apple and Google and others all encourage it even when it is not actually necessary.