We stopped by Weir Farm on a nice Sunday in October. It was a great way to spend the day. The grounds are beautiful. The visitor's center is staffed by Rangers. Our two children (4 and 3) enjoyed the Junior Ranger programs. We did the Pond Pack and the Letterboxing activities.
The Pond Pack was fun, they give you a Junior Ranger backpack with supplies (tape measure, magnifying glass, bug box, sketch pad and a field guide for identifying things). Then you go for a short hike (45 minutes) through the woods on an easy trek to the pond. The trail loops around the pond and comes back. We found the dam to be a good place to picnic. We then headed back to the visitor's center and did the letterboxing, about another 45 minutes. The kids get a badge for completing one exercise and a patch if they complete both.
Also, on Sundays they put out a nice tote with water color painting supplies. The kids painted while at the pond and also back at the farm. The houses on the Weir Farm weren't open when we were there. It looked like they were being restored. We spent about 4 hours total on the property.
There is a little gift shop in the visitor's center with an orientation video. There are also clean bathrooms attached to a barn out back. We didn't see any place close-by for food, but it didn't matter for us because we packed a lunch. We got into the main parking lot at around 11:00. It was about 1/2 full. They have over flow parking and the Rangers were right on top of letting people know where to park.
I highly recommend a visit.