I'd say it depends on whether this colleague can help or hinder your career in some way. I never received any college graduation gifts from my parents' colleagues, but if this child is close to you in some way and/or the parent is someone who can have some impact on you personally, I'd give $50-100.
IMO it's not worth giving this gift unless you give at least $50 - this person is a college grad, not a HS grad, and a $25 gift may be taken worse than no gift at all.