Hi Heather, just got back from Cuba last week. The Cuban currencey is closed so you can't buy any out of the country. Also tourists use the CUC the Cuban convertible which is valued at 25 times the Cuban peso, as their wages are so low. (1.50CUC to the £)
Had a great time there, makes you appreciate all we have here though.
Please make sure you have toilet paper with when you're away from the hotels & the children etc need pens, pencils, toothpaste, toothbrushes, soap (take this from hotels) & clothes are also appreciated.
Enjoy your trip, a fascinating country with music everywhere you go.
Mo