£12 a month Samsung Galaxy Fame + Samsung Galaxy Tab 3 7 inch 8GB WiFi -any good

The Moto G, as Grumbler suggested, would be my choice in your circs as it's a VERY well made phone and even has the latest Gorilla Glass screen (3). And I would always be tempted to buy outright and pair it with a SIM deal that was at most a 12 months commitment (ideally 30 days) as youg ones' mobile needs can change dramatically in the space of a month let alone 24 and this would give you much more flexibility going forward. And i would get the best phone you can afford/are willing to pay for at the moment and add a tab at some later stage. But you are in luck because you can now get a mid priced pohone for budget money (the Moto G!).

PS Over the course of 24 months the upfront cost of the Moto G works out at £3.70/mth. Add the 30 day Tesco £10 SIM (500 mins, 5000 texts and ONE GIG of data) to that phone for a superb, flexible mobile package. Effectively £13.70/mth. 250GB data for a teenager is cutting it very fine IME.