CAT
My understanding is as follows (but I'm not a tax expert):
If you just give them the cash in a lump sum (say €40k each) it will fall below the threshold for capital acquisitions tax (CAT), which is €456,438 for a son/daughter at present. However, if they later inherit or are gifted more money from you, this will be added to the €40k given now in order to see how much of the cumulative sum received is over the threshold.
However, you can give them €3,000 per year outside the tax system (i.e. it doesn't contribute towards the cumulative sum received that brings them closer to the threshold).
So if they don't actually need a lump sum now, it would be more tax efficient to give them €3,000 p.a. each on an ongoing basis - or maybe depending on your age/their age, some of the money as a lump sum now and the rest as €3,000 pa in subsequent years.