Purim Katan ("little Purim") occurs on the 14th and 15th of Adar I, which is only during leap years, such as the current year.
Mishnah Megillah 1:4 says:
קראו את המגילה באדר הראשון ונתעברה השנה, קורין אותה באדר השני. אין בין אדר הראשון לאדר השני אלא קריאת המגילה ומתנות לאביונים .
If the Megillah was read in first of Adar, and the year was [subsequently] intercalated, we read it in second of Adar. There is no difference between the first Adar and the second Adar except the reading of the Megillah and alms to the poor.
The Mishnah does not mention anything about mshlo'ach manot - the exchanging of food gifts even though it, as well as making a festive meal are mentioned in Esther 9:19:
עַל־כֵּ֞ן הַיְּהוּדִ֣ים הפרוזים [הַפְּרָזִ֗ים] הַיֹּשְׁבִים֮ בְּעָרֵ֣י הַפְּרָזוֹת֒ עֹשִׂ֗ים אֵ֠ת י֣וֹם אַרְבָּעָ֤ה עָשָׂר֙ לְחֹ֣דֶשׁ אֲדָ֔ר שִׂמְחָ֥ה וּמִשְׁתֶּ֖ה וְי֣וֹם ט֑וֹב וּמִשְׁל֥וֹחַ מָנ֖וֹת אִ֥ישׁ לְרֵעֵֽהוּ׃
Therefore do the Jews of the villages, that dwell in the unwalled towns, make the fourteenth day of the month Adar a day of gladness and feasting, and a good day, and of sending portions one to another.
(Shulchan Aruch O.C. 697 mentions that one should make a feast on Purim Katan similar to Purim, but common custom is not to do so.)
Why aren't gifts exchanged during Purim Katan, considering that the Mishnah states that there is no difference between the 1st and 2nd Adar other than the 2 specific items that were mentioned?