Is Lego Muktzeh? and can Adults use it too?
"Any toy that needs to be screwed together is prohibited because of the issur of Boneh. Therefore, one may not play with a construction set on Shabbos. On the other hand, because one merely sticks together the pieces, one is permitted to play with Legos, Tinkertoys and the like on Shabbos."
Teshuvos written by HaRav Yisroel Belsky, Shlita
You seem to be asking two questions here:
- Is Lego© Mutar for an adult to use? How about a child?
- If it's only Mutar for a child, does that render it muktze for an adult?
(Perhaps I'm reading into your question because of the availability of my answer, but either way it will address your question.)
Hacham Ovadia Yosef, in Yechave Da'at (2:55), Addresses Lego©. (He starts off by saying that if something is Assur for adults, then its Assur for children too, yet) he seems to conclude that it's fine for children to play with Lego© on shabbat, but adults should stay away. He argues mostly that there's no melacha according to the Shulchan Aruch, but seems to be machmir for adults anyway (possibly because he is choshesh for the opinions that are machmir.) He restates this conclusion in Yabia Omer (O"C 7:39), where he says, "העלתי שמותר לתת לקטן 'אבני פלא' וכיו"ב לשחק בהם להרכיבם ולפרקם"
Regarding muktze, Hacham Ovadia in Yabia Omer (ibid.) says that Lego© is not muktze for an adult:
וגם נראה שמותר לגדול לתת לקטן לשחק בצעצועים המיוחדים לקטנים, ואין בהם משום מוקצה
Harav E. Y. Waldenberg, in Tzitz Eliezer (13:30), (also quoted in Yabia Omer, among other modern poskim that Hacham Ovadia quotes,) rules that Lego© is completely mutar, even for an adult:
בהא נחיתנא ובהא סליקנא דאין כל איסור בונה או סותר בבנית או סתירת אבני - פלא שהילדים שוחקים בהם. וגם לרבות לא משום תיקון מנא. ומותר לשחק בהם בשבת. בכבוד רב וביקר אליעזר יהודה וולדינברג.
He backs up this pesaq din in 13:31, the following siman.
If the blocks are easily removed - even adults can play it.
But if you need to apply some force in order to connect/remove the blocks it more miskaem, so there are different opinions on that case. When I asked about it my Rav he told that even in latter case there is no problem for adults to play it. However I've heard others that forbid playing hard-stucking lego to adults.
In any case, even if just children are allowed to play it - it is not a muktze.
Great answer by Baal Shemot Tovot though extra sources brought here:
R' Pesach Eliyahu Falk (Machazeh Eliyahu 69) writes that while joining two pieces together is permissible, one shouldn't even allow one’s children to play with Lego on Shabbos because building models could come under the prohibition of kesiva, and building a house with a roof could be creating an ohel.
Yet, many poskim including the Tzitz Eliezer (13:30-31) permit it. Seemingly, other poskim are primarily concerned for the prohibition of boneh. Both the Shemiras Shabbos Kehilchasa (16:18) and R' Belsky write that while construction sets that need screwing together are included in the prohibition of boneh, one is allowed to play with lego on Shabbos.
While R' Ovadia Yosef allows it (Yechave Daas 2:55 and Yabia Omer OC 7:39), he suggests that because of the above concerns, adults should ideally refrain from Lego building, though children may do so.
In conclusion, it is best not to build complete models or buildings on Shabbos, though it is okay to assist children with their Lego building
It is permitted to play with lego on Shabbos, in particular where the purpose is not to leave the construction for a long time. For lego that will be left for a long time (sometimes true for small lego), one should be stringent.
Where pieces are not fixed in place strongly, and it is normal to put them together and take them apart, it is permitted to play with lego (Minchas Shlomo 1:11).
See also Rabbi Pesach Eliyahu Falk (Shut Machazeh Eliyahu), who is likewise lenient for matters of boneh, but is stringent with regard to small lego because of the issue of “writing” (sculpting).
I have heard an opinion that it is permitted even for adults simply because the intended purpose of the Lego product is to put together and then take apart. Therefore, it's status would not change based on personal intentions or whether they are easy or hard for the user to take apart.