It is not something that should be done until at least 6months as they are still too young to understand...but also remember there are other ways of teaching a baby to self settle & during the day could be a good time to start. Also please do remember not all babies sleep great, some just need extra help ect. Also if you do go with cc & it is your choice remember to keep in mind things such as teething that will happen at this age & to always check bubs needs before leaving to cry it out.