I've bought the two Putt-Putt games for my kids (ages 4 and 7) to play together, and they have enjoyed them. They played through Saves the Zoo probably half a dozen times, but found Travels Through Time to be a bit trickier and haven't been able to finish it. My impression was that Travels Through Time has a premise that is a little less accessible for small kids, and the puzzles seem to be more esoteric - I haven't been able to help them through it! The younger kid still asks to play Putt-Putt, but the older kid finds it hard to get excited about Putt Putt when the Switch also has Mario Kart on it.
To be honest, the market for kids games is so different to what it was in the 1990s. The pace of the Humongous games is so much slower than almost any other game my kids have played on something with a screen. Modern games have an abundance of ways get instant feedback by clicking or tapping or swiping, and constant incentives to keep playing and progressing in some way or another. Compared to this, Humongous games are much slower. I would say that they are less engrossing than watching cartoons, since there are plenty of times without a lot of action, or where you might just be sitting there thinking about how to solve a puzzle. The level of engagement is more like reading a picture book, which I personally think is good for kids, but that's not where the market is.
Obviously, the market for these kids of games is parents rather than kids, but again the market is way different than it was in the 90s. I remember seeing Humongous games at Costco and electronics stores in the 1990s, but that casual retail market is gone. I honestly have no idea where to buy good 'edu-tainment' games for my kids.
Interestingly, the Humongous graphics and sound have held up better than I expected. My seven year old nearly started to cry when he saw what Mario Kart 64 looked like, but had no complaints about Putt-Putt.