Dry Hands for Netilas Yadayim

Question: Do I need to ensure that my hands are totally dry before washing them before eating bread?
Answer: The Gemara (Shabbos 14b; Eruvin 21b) teaches that Shlomo Hamelech instituted the mitzva of washing one’s hands before eating teruma, as one’s hands may have come into contact with items that are tamei, ritually impure. According to the Gemara (Chullin 106a), this law was extended to everyone washing before eating bread, so as to ensure that kohanim would become accustomed to wash their hands before eating.
There is a machlokes, however, as to whether one needs to ensure that one’s hands and the cup handles are dry before washing.
The Rema (OC 160:11) quotes the Terumas Hadeshen (259) who holds that a basin of water which has been touched is suitable for use for washing one’s hands. Only water that one used to wash one’s hands with, becomes tamei and unfit for use again.
Following this, the Chazon Ish (OC 24:20) writes that if one’s hands were wet before washing, the water on one’s hands becomes tamei, and does not become tahor by being washed. As this invalidates the washing, both one’s hands and cup handles need to be dry before washing.
However, the Magen Avraham (162:10), Mishna Berura (162:27; Biur Halacha 162:2; Shaar Hatziyun 162:41) and R’ Benzion Abba Shaul (Ohr Letzion 2:11:9) write that one does not need to ensure that ones hands are dry before washing. The Mishna Berura quotes the Pischei Teshuva who writes that one should ensure that the cup handles are dry before one touches them. Nonetheless, he disagrees, writing that this water does not become tamei, and therefore it does not invalidate the washing (See Eretz Zvi 35).
In conclusion, one may wash one’s hands even if they are wet, though many are particular to ensure that they are dry first.

Children Affixing Mezuzos

Question: Our eleven-year-old son asked if he could fix the mezuza onto his bedroom doorpost. Is this permissible?
Answer: The Shulchan Aruch (YD 291:3) writes that children are also obligated in the mitzva of mezuza and we should train them (chinuch) to affix mezuzos on their doors.
R’ Yaakov Yeshaya Blau (Chovas Hadar 1:25) explains that the Shulchan Aruch is clearly referring to a house that is only inhabited by children. If the child is able to, he or she should affix the mezuza, though doing so is only a mitzva derabanan of chinuch. He questions whether an adult doing so on their behalf would recite a beracha or not.
R’ Avraham Dovid Wahrman of Buchach (Daas Kedoshim 289:2) writes that if a mezuza falls on Shabbos, one can get a child to affix it on Shabbos. Nonetheless, in his notes (Gidulei Karka) he questions whether children can be trusted to have the appropriate intentions as they affix them.
R’ Eliezer Waldenberg (Tzitz Eliezer 14:75:1) notes that there is a machlokes as to whether children may affix by themselves or not, and concludes that they may not affix mezuzos. He explains that even the Shulchan Aruch means that children should have an adult affix the mezuza on their room on their behalf. If a child does hang the mezuza, it should be removed and reaffixed by an adult.
In conclusion, children should not affix mezuzos until they are bas mitzva or bar mitzva.

Scooters on Shabbos

Question: Can my children ride their scooters on Shabbos where there is an eruv?
Answer: R’ Ovadia Yosef (Yechave Daas 2:52; Yabia Omer OC 7:37:3; 10:55:2) quotes the Ben Ish Chai (Rav Poalim OC 1:25) who permitted cycling on Shabbos though writes that the consensus of acharonim is that cycling is prohibited for various reasons.
R’ Ovadia Yosef quotes acharonim who are concerned that the tyres will leave grooves in the earth which is prohibited due to choresh plowing. The Kaf Hachaim (OC 404:8) writes that when riding a bike, it is very easy to mistakenly ride outside of the techum or carry it out of the eruv. In addition, it is common for things to break which could easily lead to the prohibition of tikkun mana, fixing things. R’ Eliezer Waldenberg (Tzitz Eliezer 1:21:27; 4:4:8; 7:30) adds that using a bike is also prohibited because it is uvdin dechol, a mundane, weekday activity.
As children’s tricycles are not used to ride long distances, R’ Yaakov Kamenetsky (OC 302:339) did not consider them to be the same issue of uvdin dechol and allowed children to ride them on Shabbos. Likewise, R’ Moshe Feinstein (quoted in Tiltulei Shabbos 1:n21) differentiated between bikes that are used for travels and kid’s tricycles that are not typically ridden for long distances (See Baer Moshe 6:16; Ohr Letzion 2:42:1). Similarly, R’ Yehoshua Neuwirth (Shemiras Shabbos Kehilchasa 16:18) forbids children from riding bikes though writes that they may ride tricycles and scooters.
In conclusion, while adults may not ride bikes on Shabbos, children may ride on scooters.