Empathy of Useful Feedback
If a friend shows a work-in-progress, the best thing you can do is imagine the perspective and preferences of the person who is creating it. It’s not helpful to say “I don’t like it” because you aren’t the intended audience. “I can imagine someone who wants …” would be searching for x,y,z” is more helpful.
It is not necessary to be 3 years old to design toys. You can also give feedback to a new toy design at any age.
When a friend brings you a finished product, you should find at least two positive and truthful things to compliment. It’s a great thing when someone shares their work with you and they care enough about the world that they want to see it progress.