Wedding thank-you note etiquette?

We got married 2 months ago and are just about finished with our thank-yous. However, on the compiled list of guests and the gifts that they gave, we mistakenly wrote down a family's name without the gift next to it. (I THINK that they gave us money but do not remember the amount.) The family happens to be good friends of my parents. Should I have my parents ask them what they got us so I can be specific in the thank you card, or should I send them a thank-you and explain the mishap?