If your child was age 18 or younger at the end of the year or if your child is a student and age 23 or younger at the end of the year and they are not providing more than half of their own
support, you can still claim them as a dependent on your tax return.
You should help them prepare their tax return to make sure that they check yes on the box "Can a parent (or somebody else) claim you as a dependent on their tax return?" If they do not mark this properly, you may have issues filing your return and your child may need to file an amended return.