Definitely look on MSE. However, I agree with Ilovecheese - think very carefully about treating grandchildren equally.
You may wish to consider how much you can set aside monthly, and possibly set up a trust to be divided in the future.
Simplest is to say in your will that the money 'In Toytown Bank account # 1 is to be divided between grandchildren' but some people want to take tax advantages by setting up trusts.
You need to consider what happens if you get several grandchildren. Also, even if you can afford to put aside a monthly sum for each, how do you even up at your death if they haven't all reached 25?
These can all be dealt with, but need some thought.
I personally am wary of IFAs but that's probably because I don't have enough money to make it worth paying them!