Sorry, this deal has now expired. No need to worry though as we have plenty more deals like it for you to choose from...

Up to two children under 5 can travel free with every adult ticket purchased online at thetrainline.com.
You don't need an online discount code to take advantage of this offer, simply visit thetrainline.com to book your tickets for your required journey.
Once you have your tickets you can take up to two children under 5 free of charge using your adult ticket.
Please note that children under 5 travelling for free may only occupy a free seat that is not required by any fare paying passenger, so may need to stand or sit on your knee if the train is busy.
Children under 5 can also travel free with an adult ticket purchased at your nearest train station, or direct from the train company website.
| Related: |
This is not a deal. All passengers, no matter where they've bought their tickets from (that means it could be from a station or another website), are entitled to bring two under fives along free of charge. The only restriction is that during busy periods they could be required to have the children on their lap so that fare paying passengers can use the seat. Let me say again, this is not a deal, it is not unique to The TrainLine and you can do exactly the same with any valid ticket no matter where it's purchased.
Source: National Rail Conditions of Carriage, Condition 5 Children. http://www.nationalrail.co.uk/times_fares/nrcc/NRCOC.pdf
Thanks foxbat, you're correct, I've updated the deal's terms and conditions to make this clear to everyone.
But more importantly, it is not a "deal" at all- the article still makes it look this a thetrainline deal, when in fact booking through them is likely to cost the people who take advantage of this "deal" more due to booking and postage fees that thetrainline charge
Kids under 5 travel on the train for free anyway so how is that a deal ?
Don't buy tickets from TheTrainLine, it's a rip-off! Pretty much all of TheTrainLine's advertising is misleading. They imply that they sell cheap train tickets, but the fact is the price that TheTrainLine charge for ANY ticket they sell is EXACTLY the same price as tickets bought from a railway station booking office or from any of the train company's websites*. The only difference is that TheTrainLine whack a booking fee on top of the price, and charge a postage fee. So in reality a more truthful statement would be to say that TheTrainLine sell dearer train tickets! This also is true of the advance tickets they sell. The same advance tickets are available from the booking office, or train company's websites*, for the same price, minus the booking fee and postage. It is also worth noting that you can use any train company's website to buy the full range of tickets for any other train company's services, you do not have to buy from the company you are travelling with. So for example you could use ScotRail's website to buy a ticket from London to Penzance. This is also true of booking offices, you can buy a London to Penzance train ticket from Glasgow railway station if you wanted.
In a nutshell, if you buy a ticket from TheTrainLine, then you have paid more than you needed to. They DON'T sell any tickets cheaper than anywhere else.
*Some train operating companies also charge booking fees and postage, but the vast majority don't. RedSpottedHanky also don't charge any extra fees or postage.