I love those moments in a play-based class where academic learning slides easily into child-led play.
In our sensory bin, as far as any adult knew, we had: colored rice, scoops and toy animals. Then, a child discovered there were also letters in there! Alphabet soup noodles dyed in colors that almost matched the rice. You had to look really close to spot them.

He and I collected them for a few minutes – he was gathering them all in one hand while searching with the other.
I wandered on to play with other children.
Quite a while later – maybe 10 or 15 minutes – he was still at the sensory table, searching for letters and gathering them in a cup. This was great fine motor practice and close observation practice!
I sat at the snack table with other children. He brought over the cup of letters to show to me. I asked his permission to pour it out on the table, and then we sorted it to see if we had the whole alphabet.
Lots of other kids at the table got involved in recognizing the letters, and singing the ABC song repeatedly to help us put them in the right order.

We noticed that we were missing a few letters so he and two other kids headed back to the sensory bin together on a quest for those letters – as they brought their finds over, I asked where they fit in the alphabet and if we already had that letter. We were still missing 3 letters, V, S and D.
Another child wanted to get involved, but she doesn’t know letter shapes yet, so was having a hard time discerning them from the rice. I showed her the dark blue letters, which were the easiest to spot. She went over to help the others search and in the end, she was the one to find all three of the final remaining letters.
We all celebrated when our alphabet was complete.
If I had set out to make a lesson plan to teach letters and alphabetical order that day, I could never have come up with as great of a learning activity as the children found for themselves, with just a little scaffolding from me.