In the middle of the last month, I went to a show-and-tell session of nature observation activitylast month/halfway through last month/ Midway last month , I went to / (participated in) a show-and-tell session about observing nature.

giving some alternate expressions

My elementary school granddaughter, a 4th grader living in Tokyo, takes part in theis kind of activity.

id say this would be a bit more natural to say than previously

InDuring the session, elementary and junior high students made presentations in earnestearnestly presented about the ecology of wild birds around the Tamagawa River and various other organisms in tidal flats.

some changes in grammar and additions of words to make it sound like the sentence flows better, i feel.

They had conducted the research for a year.

Listening to the presentation with/ whilst being accompanied by my husband, I was impressed by how they conducted the research:; those kids took a huge interest in the immediate nature and continued the research from different perspectives.

accompanied I feel isnt appropriate for this sentence. With is better. Because accompanied on its own in the original sentence (Listening to the presentation accompanied by my husband) makes it sound like the presentation and the husband are something together. Eg. the use of accompanied can be as follows. "The music was accompanied by the sound of my kids screaming behind"; it kind of links the music and the screaming in some sense that I don't think fits for the sentence written. Also i think ; is used rather than : here. ":" is like a cause and effect, e.g. I looked over and it revealed something shocking: a dead body. ";" is like adding on information.

It seemed to me that they had much affection for local nature and that love could be traced back to their impulsepassion for exploration.

some additions just to enrich the sentence. mm i dont think impulse is appropriate for this. Impulse gives a negative tone at times, eg. impulse to push him away because I was angry. Maybe look up synonyms for affection and see the different words that could be used instead of affection, i feel there are other nicer words.

Their spirit of inquiry gave me the increasing expectation that they would in turn/ eventually become curious about global climate such as global warming and move toward solving the problems.tackling/ facing it.

some expression additions, nothing too wrong with the original.

Our yard is crowded with/ full of/ frequently visited by a large variety of wild birds.

additional expressions. But there is a new nuance in "frequently visited"; it adds time element to it that the other phrases don't.

Before now, I just saw them absent-mindedly./ without much thought/ I would (look/ observe) them without much thought

alternate expressions.

However, if I see them as if I were one of those kids, I might be able to make a discovery./ through the lens of one of those kids, I might be able to make a brand new discovery or revelation.

revelation is like enlightenment, similar to discovery but more strong of a word I think. perhaps the phrase "through the lens of one of those kids" could be a better expression here, because it sounds like you are saying if you were one of those kids seeing it. So this phrase "through the lens of" is quite a nice phrase you can use for a variety of cases. E.g. "if you look at the problem through the lens of person X, it may seem different.", "if you look at the picture through another lens, you can see that it gives off a different feeling"

An inquiring mind can add beauty to a casual/ monotonous/ simple daily lifestyle, which is what I learned from the session.

In the middle of the lLast month, I went to a show-and-tell session ofwithin a nature observation activity.

"In the middle of the last month" isn't wrong, but also isn't a phrase that we use

My (elementary school) granddaughter, a 4th grader living in Tokyo, takesook part in the activity.

This took place last month, so use past tense.

"Elementary school" and "4th grader" imply the same thing, so you can leave one of them out, but I think using "4th grader" sounds more natural.

Listening to the presentation accompanied by my husband, I was impressed by how they conducted the research:; those kids took a huge interest in the immediate nature and continued the research from different perspectives. / My husband accompanied me to the presentation. Listening to it, I was impressed by how they conducted the research....

My personal choice, I'd split the sentence since the part about your husband isn't really related to the rest of the sentence.

It seemed to me that they had affection for local nature and that love could be traced back to their impulsdesire for exploration.

"Impulse" means a sudden desire to do something. An impulse isn't something you give a lot of thought to.

Their spirit of inquiry / inquiring spirit gave me the increasing expectation that they would become curious about the global climate, such as global warming, and move toward solving these problems.

Before nowthen, I just sawlooked at them absent-mindedly.

"Look" might be a better word since it is more active than "see".

However, if I seelook at them as if I were one of those kids, I might be able to make a discovery.

In the middle of the lLast month, I went to a show-and-tell session of a nature observation activity.

My elementary school granddaughter, a 4th grader living in Tokyo, takesook part in the activity.

They hadspent a year conducteding their research for a year.

Their spirit of inquiry gave me the increasing expectation that they wouldmay become curious about global climate, such as global warming, and move toward solving the problems.

Before now, I just sawlooked at them absent-mindedly.