There's not a lot I can add to what the other reviewers say, they got it right. If you are somewhere nearby and have an 30 minutes to an hour to kill, Webster Pond is worth a visit. I don't think you'd find enough here to spend several hours, but still it can be a pleasant stop to or from somewhere else, and you can't beat the price (free, unless you buy feed for the birds).
You can buy food to feed the ducks, geese and swans, but in my observation, by late afternoon, on a day where there have been many visitors, the birds aren't that hungry any more and might ignore your offerings. If you want the kids to get a kick out of feeding them, coming earlier in the day might be advisable. And please, do not bring bread, crackers or anything else to feed them. Stick to the food you can buy at the pond; it is better for the birds.
Here's one suggestion that works great for us. Prior to coming to the pond, stop by at Gannon's (only a few blocks away) and buy a cone or dish of ice cream to take with you to the pond. No, it's not for the ducks, it's for you, to eat on a bench or in a car as you enjoy watching the birds.