Is a gift from parent to adult children taxable to children?

Not if it is a true gift.

People often misuse the term "gift" to disguise some other type of payment that may be taxable. For example, if you spend 40 hours a week digging ditches and at the end of the week the person who told you to dig gives you a "gift," calling it a gift does not change the fact that it is a taxable wage.

And you may have to pay tax if you dispose of a gift of appreciated property. Let's say your parent bought stock for $1 a share some years ago and gives it to you. You won't pay tax on the gift itself, but if the stock is now worth $100 a share, you will pay tax on the $99 difference when you sell it. Unfortunately, it doesn't work the other way around. If your parent paid $100 for the stock but it is worth $1 on the day of the gift and you immediately sell it, you don't get a $99 deduction (capital loss).

There may be some cases in which the IRS can reclaim part of the gift. For example, if the gift constituted a fraudulent transfer to evade paying tax or if the parent does not have enough assets remaining to pay any gift tax that may apply.