My husband has a 14 year old. He has a separate term assurance policy where the proceeds are paid directly to her if he dies before she is 25. Our wills then leave everything to other spouse and divided between our own children on our death.
Solicitor advised that this was the easiest option. No obligation after age 18, but we will review once term assurance policy finishes.
No obligation for me personally to leave anything to her. OP , I would advise getting a will made.
Once the dependents reach 18 there is no obligation from anyone to leave them anything.
Equally they have no rights to anything.
However, Sect 117 of the Succession Act, in part, says the following:
"...Where, on application by or on behalf of a child of a testator, the court is of opinion that the testator has failed in his moral duty to make proper provision for the child in accordance with his means, whether by his will or otherwise,...."
http://www.irishstatutebook.ie/1965/en/act/pub/0027/sec0117.html#sec117
I have first hand experience of this being used by adult children to lodge a claim based on different schoolings: Loreto College versus the local VEC.
The process was kicked off by a simple Caveat and the only ones who made money were the lawyers on both sides.
I am not saying it is right or wrong, but it cost a lost of money.
As the saying goes, where there is a will there is a way...
In most cases the family home is the main asset and in extreme cases of exclusion planning, I have seen the house sold to the non-step children with a lifetime interest to the parents. I gather than if this exists for more than two years, it cannot be attacked by the "excluded"
My point is that making a will without thinking through the different permutations can lull one into a false sense of 'legal security'.