Since someone mentioned it, my immediate family is quite keenly aware that I have Tamagotchis and I play with them without reserve in front of my family. One of my aunts and uncles knows I collect Tamagotchis - in fact they were quite pleased I still had the first one they gave to me - and so does a good friend of mine and her husband - who immediately recognized them from when their children had them. Another thing to note is that good friend already knew I collect dolls and make doll clothes and watch anime/read manga so a quirky Japanese toy is not really that peculiar. Perhaps dolls are a bit more childish than Tamagotchis and so far my immediate family, most of my extended family, and a few friends know that this is one of my hobbies, and I have yet to hear a negative word about it. Tamagotchis can't really be any less childish than dolls that are specifically designed for young adolescent girls.
I take my Tamagotchis with me when me and my father go on our evening walks and always to church - whether I'm just listening to the sermon, working in the kitchen, or teaching ESL. Mind you, my tamas are always in my bag at church with the sound off, I always use them in my bag and don't take them out, and I never really speak of them. But I have taken them out occasionally for a quick glance and no one ever pays much attention and my usual sermon setup is having my tamas visible at the base of my bag. I don't think anyone can see them from the pew behind, but a greater test was when I was muting the sound near the start of the sermon and no one really reacted (although what would anybody do anyway?).
So, the short answer to your question is yes, I do play with my tamas in public but only for short, occasional moments where they are then returned to my pocket or bag. I also want to mention that as I came to realize quite clearly from
this topic here, allot about how you treat your hobby determines the impression others get from it. So if you treat your hobbies like they are awkward or childish, or in a bizarre twist of social etiquette feel you must be apologetic for them because that is what is expected of you, you will always create a negative impression. But if you express the simple joy and enthusiasm you have for your hobbies, you will create a positive impression.
Suffice to say I'm a little anxious about being perceived as childish because I've been a social oddity by being part of the younger age bracket but acting, looking, and being perceived like I'm part of the older one (and I've shocked a few people who didn't know I was really that young). Add to this how it is such a huge compliment for me to be praised for my maturity, and the fact that I collect dolls and enjoy children's tv shows sounds problematic. But, whether something is childish or not does not depend on whether it is made for children, but
the reason for liking it. This is because all opinions are not based on facts but on feelings, and thus the quality of the opinion depends on the quality of the reasoning that formed it. Opinions are not set in stone like facts because a person chooses what to focus on and what to ignore, solely because they have decided to. If one has childish reasons for like something, then that subject is childish. But if one has intelligent reasons for liking something, then that subject is intelligent. As such somebody can like something made for children without they themselves being childish, because their discussion will not contain childish ideas.
But above all, the one who determines whether something is childish, or mature, or anything else is the person themselves. If they are convinced that their reasons for doing something are such, then that reason truly is that way. All things can be perceived differently by different people but what truly matters is one's intentions, the reason for which they act. People can only observe what they see but the individual knows innerly why they act. Thus the one who is limited is outsiders and they cannot give an opinion better than one's own because the individual knows more than they do. To sum it up, in essence you are your own judge and if you know your intentions, you do not need anything else.