May children or adults draw pictures and make paintings on Chol Hamoed?
It is forbidden to write [or draw pictures or designs] on Chol Hamoed. Some Poskim rule that it is only forbidden to write in a professional script, known as Maaseh Uman, which is the scribal lettering used for writing a Sefer Torah, Mezuzah and Tefillin [i.e. Ksav Ashuris]. It is however, permitted to write in a commonly known script [i.e. Maaseh Hedyot] on Chol Hamoed [so long as it has a need for the Moed]. However, other Poskim imply that even amateur writing is forbidden to be done during the Moed, as all script was considered by the Sages to be professional. Practically, we rule like the former opinion. From the letter of the law, this script may be written even without an irregularity/Shinuiy, however, the widespread custom is to write it with a Shinuiy.
It is permitted for children or adults to draw amateur pictures, drawings, and paintings on Chol Hamoed as a fun activity for recreational and entertainment purposes. However, a professional picture or painting may not be done.
 See Admur 340:10 “One who makes marks and designs on a document and the like, in the way that the artists design, is liable to an offshoot of the writing prohibition. The same applies for one who erases it.” See also Admur 519:6; M”A 340:6; Rambam Shabbos 11:17; Degul Merivava 340; Tehila Ledavid 340:3
 Michaber 545:1; Rambam 7:13; Mishneh Moed Katan 18b; Smag Lavin 75:28
The reason: As this is considered a Melacha which does not have a need for the Moed. [Rambam ibid; Smag ibid; Beis Yosef 545]
 Beis Yosef 545:5 based on Rif, Rambam, Rosh, Ravad, and Ramban who all permit writing letters and Cheshbonos “Practically, the Halacha is…that one may write letters [in regular writing” even without an irregularity”; Bach 545 “It is obvious that the Sages only prohibited the Ashuris scribal writing during the Moed and not any other form of writing that we do today”; Rabbeinu Tam; Agudah; Rabbeinu Yerucham Tolkdos Adam Vechavah Nesiv Daled 5 in name of Rabbeinu Tam; Orchos Chaim Chol Hamoed 7; Taz; Kneses Hagedola 545:1; Olas Shabbos 545:1; Elya Raba 545:5; M”B 545:35; See Michaber 545:5 regarding Sheilas Shalom and Prakmatya; M”B 545:4 and 30; See M”B 545:4; Rama ibid regarding writing for a public need that is not for the need of the Moed writes “The custom is to be lenient regarding our script of writing which is not Maaseh Uman”
 Implication of Bach ibid that only if it is for the need of the public may it be written for after the Moed; M”B 545:30; Chol Hamoed Kehilchasa 6:8 footnote 19; Piskeiy Teshuvos 545:1
 Implication of Terumos Hadeshen 85, brought in Bach ibid and Beis Yosef 545, who forbids writing even for the sake of the public, even in a regular script; See Kaf Hachaim 545:11
 M”B 545:30; Chol Hamoed Kehilchasa 6:8 footnote 19; Piskeiy Teshuvos 545:1
 Bach 545; Kneses Hagedola 545:1; Olas Shabbos 545:1; Elya Raba 545:5; Rama ibid regarding writing for a public need that is not for the need of the Moed; See Kaf Hachaim ibid
A place without a custom: In all areas without a set custom, those who are lenient to write regular script without any irregularity , have not lost out. [Darkei Moshe 545:4; Elya Raba ibid; Kaf Hachaim ibid]
 Chol Hamoed Kihilchaso 6:84 “Children who draw and color, there is no prohibition involved at all” and Footnote 197 “This is obvious”; Shemiras Hamoed Kehilchaso 8:12; Piskeiy Teshuvos 545:12
 The reason: As since they enjoy this activity it is considered for the need of the Moed [See Michaber 536:1], and it is permitted to write amateur script for the sake of the Moed. [See Poskim ibid in background]