Children are an Amanah (trust) to us as Muslims and the best gift a parent can give to a child is a proper upbringing.
"When a person dies, his deeds come to an end, except for three: ongoing charity (Sadaqah Jariyah), the knowledge that is benefited from, and a righteous child who prays for him.” (Sahih Muslim)
If a person leaves pious children, he will continue to receive rewards as long as his children keep on doing good deeds, regardless of whether they make the intention of sending the rewards to their parents or not.