I normally give my niece and nephew $100 for birthdays and $100 at Christmas, I also contribute, on an automated schedule to their 529 plans during the year.
But, my nephew just turned 18 and I gave him $200 for his birthday because I counted it as a bigger birthday. He is also graduating from high school this year and I assume I will give him money at graduation. My niece is turning 16 this year and I'm pretty sure I gave my nephew $100 when he turned 16, but I don't really remember. I was planning to give her $100, plus I bought her a special necklace last year that I've been saving for her sweet sixteen. The necklace cost at least $100.
So, am I safe giving my nephew $300 this spring, between his 18th birthday and high school graduation, and giving my niece $100 plus necklace? When my niece hits 18 and graduates from high school I plan to gift to her in a similar fashion.
I should, of course, mention that there are both mature, good kids who will be happy with anything I give them and will send appropriate thank you cards too.