A pleasant piece - nice gift. Well done.
Like MJFOBOE I have a few suggestions - more about your style of orchestration as manifests in this piece. But...it's your work and if you feel happy with the style, great. You're the arbiter here.
So all I have to say are things to bear in mind for the future.
Like:
this is a delicate, pastoral piece and still seems over-heavy on the scoring. Bar 9 clarinet doubling the oboe. Yes, it calls for a different timbre at that point but have you thought about handing the solo over to the clarinet alone or leave it as the oboe alone. Ordinarily I wouldn't comment because the unison of these instruments creates a different timbre, sure but the side effect is reinforcing the sound - here, the thickness.
Same with the imitative entries on flutes and bassoons. May be better just to have one of each playing - you're asking for pp so à 2 seems an unnecessary thickening. If you suddenly wanted f or even mf doubling them might be justified but at pp?
Not sure how the brass is laid out - no player names but assume from the key sigs the top pair are horns, the lower pair trumpets in Bb. Again, do you really need horn 2 doubling an octave below? Though an excellent horn player could make those lower notes sound sweet, again with the rest pp, they'd probably sound intrusive. (If compelled to this arrangement for some reason, I'd ask the players to stuff their hands up the bell to muffle the effect a little).
Next, giving the double basses independence. There's nothing wrong with this but be cautious particularly if they're close (in interval) to the cellos, and deep - they'll sound muddy, no matter what dynamic. In some contexts this is useful but that doesn't seem the case here. Again, I could be wrong. It's a nocturne and dark-ish so if you're happy with it, fine.
A few bars later the basses double the cellos an octave down. This gives a solid bass even if quiet.
By the way, what's going on in bar 17? Is the cello supposed to be playing in the alto clef? As you've written Viola and Cello, they're parallel minor 7ths apart through 17 and 18. With the basses at parallel 6ths beneath, the harmony is going to get pretty confused. You may get away with it with rendering from notation software but in real life it could mean trouble (were this work to be performed live - and don't dismiss that it won't!)
For all that, this composition, the canonical interplay of parts is pretty clever. You do seem to have a knack with this kind of thing. And an orchestral feature you've picked up well is how you've marked the bass with the pizz basses and cellos in the opening.
When you post the following pieces, please add bar numbers per 10 or whatever or rehearsal letters! Cheers.