Is this situation a problem of yichud. I watch my kids in the morning and wait for the babysitter to come so I can go to shul. Sometimes I help my children for a little even if the babysitter is present. Also, when I get back from shul, I am home for a brief moment while the babysitter helps me prepare my children for the day. I then bring one child to groups while the babysitter takes the other child to her home down the street. I never lock the door, but since my wife is at work, the chances of anyone coming up my apartment stairs is very slight. I live in a two story attached apartment. So only my family usually walks up the stairs to the second floor. Are these few moments a day with the babysitter and myself in the apartment an issue of yichud with an unlocked door. What is the best solution?
For certain ages (approx. between 6 and 9), children will serve as shomrim, and there will not be any issue of yichud.
If this doesn’t apply, it will be best to leave the front door slightly open, so as to ensure that there is no issue of yichud.
Although the yichud is only for a short time, whenever it is possible that the yichud will extend for a longer time, the situation is prohibited.
For more details on the subject, please see https://dinonline.org/2011/12/11/laws-of-yichudseclusion-1/, and the second shiur on the same subject https://dinonline.org/2011/12/11/laws-of-seclusion-2/.