Agreed with what already has been suggested.

An important step is getting rid of most of any wax that may have been applied. Some panelling came with a wax (or something else "waxy") surface treatment, and people have been known to try to "freshen" imitation wood. A simple wash with a good detergent should be sufficient. SpicNSpan is the commonly recommended "soap" in the US.

You may find the kids have decorated a spot or two with crayon etc, and any heavy marks should be at least scraped to remove anything that might come loose later.

The critical step is a good primer. If you know the maker of the panels, they may have a specific recommendation, but Kilz and/or BiN are two excellent general purpose ones in the US. If needed to cover a dark color, a second (or third) coat of primer is a lot cheaper than extra coats of paint, assuming of course that you're using a white primer (some come in transparent versions).

John