Lisa Loring
Okay, so this is what I've found out with my 'obsession' with the Addams family of the like of Wednesday and Pugsley since their ages are very different in different versions:

..::The Addams Family 1964 - 1966::..

This is first series with two young children.
Wednesday - Lisa Loring 6 - 8 years old
Pugsley - Kenneth Weatherwax 9 - 10 years old

..::Halloween With The New Addams Family 1977::..

Somehow Gomez and Morticia apparently have produced two more children that look exactly like their last named Wednesday and Pugsley aswell! They also wear the same thing!
Wednesday - Lisa Loring 19 years old
Pugsley - Ken Weatherwax 22 years old
Wednesday JR - Jennifer Surprenant about 6 years old
Pugsley JR - Ken Marquis - about 8 years old

..::The Addams Family/Values 1991, 1993::..

Now Wednesday and Pugsley are the SAME age instead of their usual 2 year gap. Morticia and Gomez have another child called Pubert (played by FEMALE twins)
Wednesday - Cristina Ricci 10 - 13 years old
Pugsley - Jimmy Workman 10 - 13 years old
Pubert - (VOICE Cheryl Chase) Kaitlyn & Kristen Hooper both 1 year old

..::The Addams Family Reunion 1998::..

Now Wednesday and Pugsley are back to being the same age! But they are a year younger.
Wednesday - Nicole Fugere 12 years old
Pugsley - Jerry Messing 12 years old

..::The New Addams Family 1998 - 1999::..

Wednesday is now around 3 years older than Pugsley!
Wednesday - Nicole Fugere 13 years old
Pugsley - Brody Smith 9 years old
Brody Smith and Nicole Fugere
Jimmy Workman
Wednesday JR