When you say someone is in safe hands, you mean they are being cared for by someone who is confident and skilled.
John is going to be operated on by one of the best surgeons in the country. He's in safe hands.
The new CEO of the company had degrees in engineering and business administration. The staff knew they were in safe hands.
A safe pair of hands is a similar expression. It refers to someone who can be trusted to do a good job, avoiding mistakes.
My boss gives me all the difficult assignments. He knows I am a safe pair of hands.
In developed countries, the average birth weight of a full-term newborn baby is approximately 3.4 kg, and is typically in the range of 2.7 - 4.6 kg.