@robriley
I guess you mean #Interrail? I've done a bit of that, including Cardiff to Athens via the Black Sea and Sofia.
If the children are 11 or younger, then they get free IR pass when an adult buys. 12+ they need a youth pass. Yes Turkey and all likely countries en route are covered.
Evergreen advice is to look up @seatsixtyone - https://www.seat61.com/Turkey.htm