Until about 3 or 4 years old, many toddlers will appear to be ambidextrous so you'll just have to keep on guessing whether your child is a lefty or a righty. But what you should know is that being one or the other is considered to be inborn, not learned as many are made to believe.
Hand dominance is greatly influenced by genetics. But if you're really curious about your child's handedness, the best way is to tempt your little one with a toy and see which hand he or she is likely to reach out with.
As your baby develops, it isn't a good idea to influence hand-preference by forcing your child to use the right hand when he/she is really a lefty. Many parents or even teachers at school for that matter will encourage the child to use the right hand only because majority of the world is designed for right-handed people. Of course, there are some disadvantages with being left-handed but being a lefty is a normal variant, not a disability. And to be completely honest, I think a child should be given the chance to develop the more dominant hand and not forced to use the wrong hand, which could be working against your child's natural development.
Young children will often experiment using both hands - that is completely normal. But just sit it out and wait patiently and let your child decide what he/she feels most comfortable with. While 90% of the world's population is right-handed, the 10% lefties are just as functional.
Helpful note: A sign of motor development problems can be looked out for if your child seems to be using only one hand before 18months old. Speak to your pediatrician who might be able to help you out.
Helpful Resource: www.babycentre.com