As a mom who had two kids in a forest kindergarten, I would not recommend the PU coated kind you show in your post. Yes, they are cheap, especially when on sale at the usual suspects like ALDI, but considering their level of durability (as if!), you’ll be replacing them so often, that they are not worth it in my experience. They can work if you have a gentle child that plays gently and carefully. If yours is more of the “all in” type, no chance. Crawling, scooting around and similar activities on abrasive surfaces will destroy these pants in no time.
We, like pretty much all other parents in our kindergarten, chose the type made of waterproof outdoor fabrics and - particularly important - thicker, extra sturdy layers on the knees and rear. It’s not just the robustness (ever seen a kid doing a knee slide on dirt and gravel?), but also the fit that’s more comfortable for active play. For slipping on over other layers , the overall-type is also fine, so it’s also about personal preference.
They were either from the typical “outdoor specialist brands”, or for older kids, workware brands like Engelbert Strauss. For very young kids, the market gets quite small, but there are a few Scandinavian brands that have both a good reputation and small sizes. Didrikson and finkid for example do.
Now, the downside is that they are not cheap, seriously. For us that wasn’t an issue, our kids had to stay warm and dry for hours even in very bad weather.
Searching second hand is a viable option here, especially as the better quality items will be in reasonably good condition when the first child outgrows them.