Her "latest hidden gem is Afternoon Tea at the Tate Britain Restaurant - wonderful Whistler murals and quite elegant setting. Fabulous value, £7.45 for two tiers of mini goodies plus an amazing range of tea".
Seems to be one of the better options for afternoon tea with kids in London as the quantities are reasonable and the price definitely preferable compared to Claridges, Ritz or Brown's. (I should know since we nearly went bankrupt once when we invited the family.)
Afternoon Tea is available from 15.15-17.00.
Which leaves ample time to enjoy the museum. I have not seen the Watercolour exhibition yet, but this review sounds promising, some are slightly controversial. Should make for an interesting visit.
And by the way, the Tate also offers an Art Trolley with paper -based activities to use in the galleries this Half-Term on Thursday, 24.2. and Friday, 25.3. from 10.00-15.00 for budding artists.