TO BE careful (with) VS. TO TAKE care (of)

The following is a common mistake students make:

You have to take care to be careful when you are at the beach all day long...don't forget to wear your sunscreen!

Tourists must take care be careful crossing the border.

TO BE CAREFUL (WITH)

We use this phrasal verb to warn others of danger, to be more cautious, or to avoid an accident.  We use the preposition "with" before the noun (an object or a person):

Ex.

1.  You have to be careful with the computer when you pack it in your luggage.
2.  My son is always careful with his toys and has never broken anything!
3.  He is also very careful with his younger brother who is only six months old.
4.  Parents always tell their children to be careful when they cross the street.

TO TAKE CARE (OF)

We use this phrasal verb to assume responsibility for others and their well-being or to be in charge of a certain task.  

1.  First thing Monday morning, we need to take care of some important business.

2.  Why don't you take better care of your brand new car?

3.  Many people procrastinate and take care of things tomorrow rather than today.

4.  Every other weekend, I take care of my nephew and niece.
5.  "It was great to see you!  Take care!"