UK Railcards: Can a 'Two Together Railcard' be used for 2 adults and a 4-year old child?

I'm looking to buy a railcard, we are two adults and one child who is eligible to travel for free.

I like Family and Friends Railcard but it is not available until I am in the UK or I have an address in the UK where it can be delivered. To use this railcard I will have to enter my child's age as 5+, which is allowed.

My child is under five. Can I still use a Family & Friends Railcard?

A: Children under five years of age travel for free so do not have to have a ticket for travel. However, at least one child in your group will need to have a child rate ticket for you to be able to use a Family & Friends Railcard. So, if the children in your group are all four years of age or younger, you can buy one of them a discounted child ticket so that any accompanying adult can benefit Family & Friends Railcard discount.

Source: Family & Friends Railcard

However, Two Together Railcard is available in digital form and it looks like i can get it instantly and that card suits us equally well, we are 2 adults who will be travelling together.

Question: We also have a 4 year old child, can we still use Two Together Railcard legally? their website does not list anything related to that.

I don't want to game the system. The only motivation of getting this railcard is the ability to receive it in digital format even before reaching the UK, but is using that card with a 4 year old child against the terms?

Edit

Based on the advice given in answer below I went ahead and bought a Two Together Railcard. Since i opted for a Digital version i entered the address of my hotel where i will be staying. I realize that the hotel may not accept mail on my behalf when I'm not there but then there is no mail to be received with a digital card.