After finally tracking down my baby book, I thought I'd post a few facts from almost 30 years ago about the triplets' parents.
At six months I was sitting in a high chair, pulling myself into a sitting position, pulling myself into a standing position, and creeping all over (cruising at 6 1/2 months). I had my two lower teeth come in at 4 months, and my upper left tooth at 6 months. I weighed 18 lbs, 2.5 oz, and was 26" tall.
Erin, on the other hand, was drinking from a cup at this age, and she started crawling at 6 1/2 months. She had her first tooth come in at 6 months, and like Arthur, she enjoyed sticking her tongue out. Erin weighed 17 lbs, 8 oz, and was 25.5" tall.
It is interesting to compare us to our children, but while it is hard to compare the timing of developmental milestones (as all kids are different), it does make it a little more tricky since the triplets were born a month early. While in many areas we were ahead of the triplets at 6 months (and probably will be in a month at their adjusted age), some things the triplets have surpassed their parents. For example, I started kissing w/ mouth open at 13 months, which Arthur mastered long ago. Betty seems to have bulked up to be more than Erin at this age, and all three of the triplets are far taller than we were.