L L.
Yelp
There is so much crap in this house you'll never see it all. DuPont added on to house more of his hoarding--err--collection. But seriously, the "house tour" will not show you all 175 rooms. And most people would grow bored anyway. You select a theme tour and see rooms relevant to that topic. In this way, you get your fill, and can return for a different portion of house if you're still interested. Admission is good for two consecutive days. Even exploring the grounds can easily take a day or more. There is a tram visit for an overview of the estate, but really there is a lot to explore.
Long time ago I was a Winterthur member a few years. Loved the member newsletter, and the lectures and field trips offered. Not sure if it's the same now, but I have a thing for antiques and architecture so it was up my alley.
At Longwood the fuss is outside. Fussiness in the environs, manicured garden garden everywhere. The only fussy interior space at Longwood is the conservatory, which is, alas, an indoor garden. But the home is quite plain, and relaxed. At Winterthur, the fuss is all indoors, and the gardens are the relaxed part. I like the outdoor energy at Winterthur. I can unwind at Winterthur a bit deeper than I can at Longwood. There have also been (on every one of my Winterthur trips) fewer guests around, which is nice.
I've done two or three different house tours. I do not recommend them for kids under middle school age, maybe high school. Even then, it would need to be a kid wanting to learn about early American furniture, and a bit into interior decorating. Other reviewers have complained about the docents being bossy and scornful. I haven't been reprimanded for any physical misstep (though I was at friggin' Nemours), but I have gotten rebuff for commenting on, or asking unwelcome genuine questions about the DuPonts. It was naïveté and curiosity on my part, though I admit to a bit of disgust for the aristocratic marriage arrangements of their era (if they've changed today). But look, who is going to take up the position of docent and fanlady in an American antiques museum other than people head over heels for Colonial china and the immortalization of the DuPonts? Who better to throw her life in front of a Chippendale should some smartalleck kid try to stick his chewed gum in the crotch of a table? So take their sometimes rigid and defensive attitudes with fitting expectations. They ARE Winterthur.
That said, I spent a lovely time at a Terrific Tuesday kids' event (Jul/Aug), chatting with the staff as they taught kids about quill pens, wallpaper murals, patterning, and paint prints. All of them I could've taken home to dinner and chatted for hours. They were truly kind and interesting, all of them. So it may depend on who you get as your guide through the house. Remember, they're also tasked with keeping idiots from collision with priceless pieces, and that's pretty stressful.
There is a kids' hands-on room for play, accessible on Terrific Tuesdays, and of course the Enchanted Woods outside. This is a gorgeous fairytale-like nook in the gardens, filled with English countryside themed playspaces. My child and all the other kids there had a ball at the Terrific Tuesday activities, the hands-on room, and in the gardens.
I recommend checking out Winterthur's events. They have a number of well developed special days. Their Point-to-point Steeplechase every May is the toast of Wilmington Derbyfolk, a fest of Lilly tablecloths draped over Bentleys, and clanking crystal, if you dig that scene. Also, many holiday treats for kids, as well as artisan fairs, etc.
My favorite favorite favorite part of Winterthur is the collection of carved wood Schimmel eagles! Schimmel had such an ornate but macabre look to his work, like Tim Burton in wood. But they remove the eagles to make way for decorations at Christmas time, so catch them another time of year.