When you go to the grocery store, allow a few extra minutes, take them out of the cart and have them help you.

I need three apples. Thanks, that's one. How many more do we need? Now we have three. One Two Three.

It gets you talking with your child more. It gives them confidence that they are contributing to a real task. Kids love to be useful. It's up to you to pick and choose those tasks in the supermarket, and everywhere else where they will be successful. Be patient, step back, and let them do as much as they can.

My area has something called POP club (power of produce?) at the farmers markets. Kids try some sort of produce, decide if they like it or not, and then get $5 of fake money to spend on produce or seedlings. It's really been interesting watching how my kids decide what to get, and how much, and negotiate the transactions. In the spring we often get starter plants for the garden. Even if you don't have such a club you might consider a "produce allowance" when you go to the market.

Not much to do with STEM, so I'll add that my youngest really likes changing the batteries in his toys, especially if a screwdriver is required.

I think human children have likely been chasing birds, much the way puppies would, since long before the dawn of civilization. As long as you teach your children to respect nature when they're older, letting a 3 y.o. chase ducks is as natural as teaching a 3 y.o. to walk. And as much of a threat to duck society as puppies are, as well.