I've taken as young as 3 months. When I took mat leave for my first we only got 12 weeks so I'm not sure if worrying about rare possibilities of SIDS is worth not taking a child over but more just personal preference of what you are most comfortable with as an individual. Older kids who aren't at risk of SIDS will be at risk of something else. The liability in this job is always going to be high. My 3 month old came to me 5 days a week for over 3 years and was my best child because I pretty much raised her those years and we had a very close bond for such a young age. Easy Peasy to get into a routine from top to bottom.