Hi, I’ve read through the info, but I’m still confused, sorry! We are travelling the other way. 3 adults and 3 children (10, 8 & 7) want to travel from Watford Junction to Euston on the mainline train (20 mins journey) on Sat 10th Feb 24. Do I need to book tickets in advance or can we just turn up and either pay at the station, or can we use contactless? I have bought oyster cards for the adults but only topped up £10 each. I’ve read elsewhere that the children would go free but when I put the info into Trainline, it says only children under 5 travel free. It’s very confusing. Any help would be gratefully received, thank you.