In the current year, a parent may gift up to €521,208 to a son / daughter without incurring or causing a tax liability, AFAIK. (See Indexed Thresholds for Capital Acquisitions Tax - 2008 - Gift and Inheritance Tax on the Revenue site for more information)
The effect of gifts is cumulative so when your children come to inherit your estate (if those are your wishes) any earlier gifts need to be added to each of their individual inheritances in order to calculate the beneficiaries tax liability at the time of inheritance. The allowable tax-free ceiling is generally increased year on year by the Revenue, as is the current value of past gifts.
I hope that makes sense.