First of all, the melody is quite evocative, and I think it paints precisely the picture you intend.
I would consider, if you are using midi to trigger the instruments, adding at least some level of sustain to the piano. The staccato sound has its uses, but in this case I think the lack of sustain is a bit detrimental to the sound. It just makes the piano sound harsh when it really shouldn't, at least in my opinion. Something like this could also be achieved by increasing the note duration, or rather, simply allowing the piano notes to ring longer in a midi editor/composer (assuming whatever DAW you use has one). If you have access to sounds or samples of ensemble horn/string/etc. sections, experiment with using those instead of solo instruments as they can take some of the sharpness out of the sound, furthering the "wetness" of the sound without actually using reverb, which can become overpowering used gratuitously. Again, these are just suggestions, and ensemble instrument sets might actually detract from the tonality that gives the piece its playful sound, especially with the horn, but its worth trying.
As for reverb, I'm sure, though I have little experience with television, that there plenty of guidelines for the wetness/saturation a piece of music should have, but I also doubt there are handbooks or the like that tell you exactly how to turn the knobs. The entire piece was quite dry, far too dry for my taste, but rather than slapping a reverb on the output channel, I would try adding reverb on each individual instrument or instrument group until the sound is still articulate, but a bit softer than perhaps it is now. Play around with pre-delays as a well as saturation, as the former can help tremendously with keeping the attack strong.
I've worked with orchestral compositions some, and this is about the best advice I have to offer with my limited knowledge. I could be off base on a lot of this, and I expect someone will chime in if I am. I hope something I said helps a little. You definitely paint the picture you intended with the music and this is a great start to a composition and mix, so keep experimenting.
All the best,
Nick
