I am not sure if you are wanting advice how to change a diaper, how to deal with these kids, or how to tell your BF "no". Changing a diaper is the same no matter what age, just the stuff inside is worse. ;o) You can always ask her to show you before she leaves. The 3 yr old will need discipline and maybe the two of you can hit it off. If you do not, then it is not your job to be his/her friend. It is your job to watch them and make sure they are safe. Sometimes it takes a stranger for a child to listen. If you are doing this for free, I would do it to help her out once or twice, if you are doing it for money, think of it as a job. The going rate is around $7-$10/ hour depending on what you do. I would go with $7 or $8 an hour if it is your friend and you will be doing it often. Try it and see what you think. Don't worry about it until you need to.