Preventing Possible Disruptions in Prayer

6. One May Not Bring to Synagogue Children Who Are Likely to Disrupt
It is forbidden for a person praying to seat a baby down in front of him because there is concern that the baby will disturb his concentration (Mishnah Berurah 96:4). All the more so, during times of prayer services, one may not bring babies and small children who do not know how to pray, since they are liable to distract the people praying. Although there is an extra pious custom to bring babies to synagogue so that they can absorb the holy atmosphere of the place, that custom refers specifically to times when prayer services are not being held.
In order to emphasize the importance of this matter, I will cite the words of the Shlah HaKadosh who writes in the name of the Orchot Chaim: "Children’s chatter in synagogue is a severe prohibition. Nowadays, their coming to synagogue brings punishment on those who bring them there, for they come to desecrate the holiness of our God’s house and to laugh in it as they do in city streets. They get up to play with one another; this one plays with that one and that one hits the other. One is happy, another crying. One is talking, another screaming. One runs here, the other, there. One relieves himself in the synagogue and everyone screams, ‘Water, water!’ There is one whose father gives him a book and he throws it down on the floor or tears it into twelve different pieces. Consequently, the noise their nonsense produces causes the people praying to lose concentration and results in the desecration of Heaven’s name. Anyone who brings children to synagogue in this way does not deserve to receive a reward for this; instead, he should fear punishment. Worst of all, the children will be raised on this bad custom and foreign habit. As they grow older, they will increase their contempt for the synagogue and its sanctity, and they will show no respect for the Torah. Additionally, when a person repeatedly sins, [in his eyes] the sin becomes permitted. Therefore, when he ages, he will not abandon his ways. In conclusion, it is proper for a person not to bring very small children to synagogue, because he will [only] lose from it and not gain. However, when the child reaches the age of understanding, on the contrary; the father must bring the child to synagogue, teach him to sit in awe and fear, not let him move from his seat, and instruct him to answer Amen and [respond to] Kaddish and Kedushah" (Shnei Luchot HaBrit, Masechet Tamid Ner Mitzvah, also brought briefly by Mishnah Berurah 98:3).
One whose child begins to disrupt the congregation’s prayer must take him by the hand, bring him outside, and continue to pray there, even if he is in the middle of reciting the Amidah (see further in this book 17:15).

7. Preventing Possible Disruptions in Prayer
While reciting the Amidah, one may not hold an object that he fears will fall, such as tefillin, a book, a full bowl, a knife, coins, or food, because he will worry that it may drop, and thus his kavanah will be disrupted (Shulchan Aruch 96:1). Even in other parts of the prayer service, like Shema and Pesukei d’Zimrah, one must be careful about this. L'chatchilah, one should not hold anything in his hand while reciting the Amidah, for it is not respectful to stand in front of Hashem while holding something extraneous (see Mishnah Berurah 96:1 and 5, based on Talmidei Rabbeinu Yonah, Taz).
Nonetheless, holding a lulav on Sukkot is permitted because it is a mitzvah to do so and it does not disrupt the kavanah in one’s prayer. Similarly, one is permitted to hold a siddur because it is necessary for prayer (Shulchan Aruch 96:1-2).
L'chatchilah, one should not recite the Amidah while standing with a knapsack on his back, for that is not a respectful way to appear before important people, and all the more so, it is not respectful to pray in that manner. However, if he is already traveling with a knapsack on his shoulders and it is more comfortable to leave it on, he may pray with it on him if it weighs less than four kabin (approximately 5.5 kilograms or 12 lbs, 1.5 oz). If the knapsack is heavier than four kabin, he is prohibited from praying while wearing it because such a load is liable to impair his kavanah (Shulchan Aruch 97:4).
Additionally, if someone holding tefillin or money fears that if he puts these items down they will be stolen, and he does not have a friend there to watch them, nor pockets in which to put them, it is preferable, b’dieved, to keep them in his hands while praying, so that he will be less troubled (Mishnah Berurah 96:6; Kaf HaChaim 7). Likewise, if someone carrying a heavy knapsack on his back is worried that it will be stolen, and he has no other choice than to carry it, he is permitted to pray while wearing it.
A soldier carrying a gun, l'chatchilah should not pray with his weapon on him, nor enter the synagogue with it, for it is inappropriate for him to pray about life and peace while wearing an instrument intended for killing. However, he may pray with it on him if he is carrying it for security reasons or guarding it from theft. If possible, he should take the magazine out of the gun, so that it will be considered less of a weapon. When, for security reasons, it is best that the gun be loaded, he is permitted to pray with the magazine inside (see Tzitz Eliezer 10:8).
A person who has a cold must wipe his nose before praying so that he needn't do so during the prayer service. If phlegm in his throat bothers him, he should expel it before praying so that it will not distract him during the prayer service (Shulchan Aruch 92:3). If he must wipe his nose while praying, he should do so in the politest way possible. Similarly, if he needs to yawn, he should cover his mouth with his hand. This is because a person who stands in prayer must be very careful to show respect for Heaven, and all actions that are considered impolite before people are also prohibited during prayer (see Shulchan Aruch 97:1-2).