I don't think so. You will probably find that you can change the holiday to some other destination free of amendment charge providing the Foreign Office are saying it's not safe to travel, but you would need to pay the cost of the holiday that you change to, as it is at the date you make the change to your booking. So if the new holiday is not carrying a free child place at that time you wouldn't get it.

At least as you are with a TO so it should be easy to organise, whereas if you had done a DIY or Dynamic Package it would be more difficult to rearrange.

I'd keep an eye on the Thomas Cook Website, they have a question on Tunisia situation which they are likely to be updating regularly (it's under travel updates)

It all depends on how Thomas Cook are viewing the situation as the advice is not to travel.