2.5 Days in Amsterdam ... Am I Doing This Right?

Was most recently in Amsterdam in Sept. Having your kids with you is obviously a significant planning factor, and I can't advise on that because I've never been to Europe with kids.
I assume this is a first visit to Amsterdam, looks like you've been researching in a travel guide and you've seen the obvious things. Obviously kids that age will have a limited tolerance for art museums.

You asked about distance. You're right, you don't have much time, so efficiency is important. Haarlem is 20-30 minutes away but it still takes time to get to the train station in both places, then get back, etc. Haarlem is often used as a bedroom/hotel location for travelers who for some reason don't want to sleep in Amsterdam, but not sure how much it will add to your trip versus the cost in time overall that it takes to go there that wouldn't be redundant to what you can see in Amsterdam, yes if you had more time but you don't.

Don't think, realistically, that you have time for Keukenhof. With a brief trip you want to avoid the easy to make mistake of trying to do too much.

And where would be the most logical slot for the Rijksmuseum?

The Rijkemuseum is like the Lourve, it really requires at least a day. For a half day or so the Night Watch Gallery and maybe the "All the Rembrandts" Exhibit. I imagine the Rembrandt Exhibit will require an extra ticket and reserved time slot. My wife and I decided that if our time was limited at the Rijkemuseum, then we would have gone straight to the Night Watch Gallery.

If weather is nice and tulips are early, Keukenhof and Haarlem

We were at the Keukenhof Gardens on April 6, 2018, according to our guide, we were about 2 weeks early from everything being in total bloom. Sort of the luck of the draw. Instead of Haarlem and Keukenhof, you might want to consider the windmills at Zaanse Schans, makes for a nice Sunday exploration. It is about 45 minutes from Amsterdam Centraal by train.

We are OK giving the Rijksmuseum less time than it deserves. Our favorite thing about the grand European museums is the buildings themselves, and I hear this is a beautiful one. They also have a 1-hour kids' audio tour, which they loved at the Vatican Museums. The trick is that because of the Rembrandt exhibit, you need to pick a time slot. While we could skip the exhibit and get a regular untimed ticket, that seems silly if we'll be there anyway.

Perhaps we'll play it by ear, and if we don't think we'll daytrip on Sunday, we'll book a timed ticket. If we do daytrip, maybe we'll pack it in Saturday evening.

OP:

Re your latest post:

There's no "timed entry" ticket for the Rijks. But it's probably good to get the ticket online in advance b/c you can then enter through the less crowded entrance (not quite skip the line); but there's no timed entry specified (it's different in this regard from the Van Gogh and Anne Frank).

And although the building exterior is notable, don't know that it will blow you away like some will in Europe. Maybe I've just seen too many architectural wonders. But notable.

We like Haarlem and used it as a "bedroom," as well as visiting some sights there, on our second trip to Amsterdam last year. But with only three days I'd suggest you stick to Amsterdam.

What I don't see in your plan, and I'd think your kids would enjoy, is a canal boat ride -- a fun way to experience the city. You shouldn't need a reservation. We used the Blue Boat line that left from near Museumplein, but there are others. If the weather cooperates, of course.