Worth the trouble to get a young traveler discount in London?

Only you can decide if this is worth it to you. I do like the idea of him having a card he is using that is not associated with your credit cards. I would be more likely just to buy an Oyster card on arrival.

Normal Oyster cards have the daily cap. I don’t think there’s any advantage to a Visitor card.

I think it’s more aimed at people who live outside London but are regular visitors. I don’t think it will be worth it for such a short trip.

You don't say how old your son is, which makes a difference.

From Gatwick into London, there isn't that much difference between Oyster and normal turn up as you go paper tickets. Oyster is a convenience, not really a money saver on that route.

The most cost effective way from Gatwick is to buy a single to East Croydon. Tap out there then tap back in on Oyster/contactless. The reason is Gatwick is in a special zone, East Croydon is in the normal fare zones.
Given the overall cost of the vacation and Oyster capping what you would save on child fares is relatively small, and you are going through hoops to achieve that.
But adding money to the Oyster is very easy at any tube station ticket machine. There are always staff around to help if you get stuck, if you do opt for the Visitor Card and add the child discount at Victoria when you arrive there from Gatwick.

The discount is 50% of the adult fare and that includes the appropriate cap level. This applies both to the pre-ordered Visitors' Oyster card and the regular one with the discount applied.

You have to weigh up whether the £7 fee for an Oyster card is less than the discounts over your visit. For many it will be but not necessarily if you are not an intensive user. You can't use it to Bath anyway which is way outside the Oyster & contactless payment areas - you need National Rail tickets for that.

At Gatwick buy the appropriate child's ticket and don't bother about Oyster & Young Visitor Discount until you get a tube station.

key question for the best answer is how old will the lad be when you are travelling. The age breaks are different on the Tube on the trains.

There are also other alternatives, but need to know the age....

Given that the OP has worked out that her son is eligible for the Young Visitor Discount I assume that he is between 10 and 15.

The Visitor Oyster card remains a waste of money for pretty much everyone. You have to order it to be sent to you so will pay postage on top of the non-refundable fee. When here in London you won't get any benefit that you can't get from a standard Oyster card beyond a few fairly useless discounts to places we probably wouldn't recommend. The regular card costs a non-refundable £7 and the Young Visitor Discount can be added on arrival just like the Visitor card. All the various caps are applied to both cards and to regular payments with contactless cards and phone and smart watch pay.

Given your son will save 50% on every journey and cap you won't need many trips to make a profit over paying full fares.

Thanks all, this is very helpful. He will be 13 at the time.

If he is 13 then you will get the Discount and cap on normal or Visitor Oysters. As on VAP's thread on the same subject could you have the Visitor Card mailed to you domestically from WA or NY?- cheaper and faster.