I asked about it this morning, and Damian's sent me an email which explains everything.
The summary is: yes, it's true; no, they're not doing it voluntarily, it's been imposed on them; and yes, it's due to new regulations about how many hours children can perform.
Damian's not going to post here, but he doesn't mind me relating the situation on the forum.
As discussed above, when working with children there are all kinds of broadcasting guidelines and regulations. They need written permission from the child's school and Local Education Authority, and a statement of fitness to attend from their doctor. Then on the day they need to be chaperoned everywhere by someone who has to record all sorts of information including how long they're performing for, when they're having breaks, and even what they're eating and drinking.
This much they can cope with, even though it's a bit of a pain in the arse. However, shortly after Eoin's appearance the production team were made aware of new, much stricter, rules. The best way for me to illustrate what they're up against is to quote the relevant paragraph from his email:
Damian wrote:
Beyond that - this is where it gets absurd. The child cannot be in our building, whether asleep, playing Countdown or whatever, for more than 7.5 hours per day - and they are not allowed in the building after 7pm. They cannot take part for more than 1 hour without a rest - and as you know, from being miked up on set, to finishing the actual show, often takes more than 1 hour. Then there are strict break regulations, which mean if they keep winning, we cannot resume recordings as per normal, we have to wait for certain amounts of time to elapse before they can carry on. They are only allowed to perform for a maximum of 4 hours in any one
day, which basically means 3 shows. They need a separate toilet - they can't use the normal ladies and gents, and they have to be escorted by their parent / guardian to the loo at all times. We don't have separate toilets. It's just become impossible for us. We have to schedule a working day for the crew. We can't say something like.........you'll be working until 9pm as normal, but if the kid keeps winning we'll be stopping at 7pm.....its just not possible. We have audiences to consider and of course, all our production costs.
So basically the broadcasting rules concerning children are no longer compatible with the Countdown recording schedule. The lack of an age barrier is one of the things that made Countdown unique among game shows, so it's sad they have to lose that. However, there is a small amount of ointment on the fly: the door is still open for children to participate in one-off specials, so it's possible Shrinidhi might appear on one of those.
And it's not true that they're glad to have this forced upon them as Clive suggested. They're "not comfortable with it at all"; it's genuinely something that's outside their control.