Virgin Voyages has a message for parents thinking of booking one of its first sailings: Leave the kids at home. 

The first ship in development for the start-up cruise line will be for adults only, president and CEO Tom McAlpin revealed Tuesday during an event at the shipyard in Italy that is building it. 

Appearing alongside Virgin Group founder Richard Branson at the Fincantieri shipyard in Genoa, Italy, McAlpin said the minimum age to sail on the 2,860-passenger vessel will be 18 — a cut-off he said was influenced by feedback from the public and travel sellers. 

McAlpin said 86% of the cabins on the ship will have balconies, which he's calling sea terraces.

Virgin's first vessel is scheduled to debut in 2020 with two more arriving in 2021 and 2022.

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Tuesday's event was an official keel laying ceremony for the first Virgin vessel, which has yet to be named. With typical Branson flair, both he and McAlpin arrived for the ceremony via a 200-foot crane drop. They were joined by Fincantieri’s Alberto Maestrini and Bain Capital chairman Stephen Pagliuca to weld ceremonial coins into the keel. 

Virgin Voyages is a venture between Virgin Group and Bain Capital.

Keel laying ceremonies are a shipbuilding tradition that date back hundreds of years. They signify the official start of construction of a seagoing vessel.

“This is a very big day for Virgin Voyages, as an exciting new holiday option for travelers starts to get ship shape," Branson said at the event. "She will be the most recognizable ship sailing the seven seas.”

A mermaid image with the Virgin logo will adorn the bow of the first Virgin Voyages ship when it debuts in 2020. (Photo: Virgin Voyages)

McAlpin and Branson unveiled an artist's drawing of the first Virgin ship's exterior. It showed a vessel with a silvery-grey hull, smoked glass and distinctive touches of Virgin red. 

Also unveiled was a mermaid design that will be at the bow of the ship. The company said the mermaid was inspired by figureheads on historic vessels and was designed by London-based artist Toby Tinsley, who also designed the feminine motif for Branson's Virgin Galactic spaceflight company. 

The three Virgin vessels will be known as the “Lady Ships”, a play on the term ‘your ladyship’ and a nod to Virgin’s British heritage, the company added. 

Virgin on Tuesday also said it was now taking $500 refundable deposits for access to an exclusive pre-sale booking period for the first ship.

Virgin has said its first ship will sail out of Miami but has yet to release itineraries.