So here are a few things to bare in mind:
1) How you treat them now will stay with them forever. Just like with all children, you are learning who you are and how people act from the moment you can process what is going on around you. If you ignore them from the start because you don't know how to communicate, then when WILL you be confident to start talking to them?
2) Find out what type of sign language they use. Makaton is common for very young children, who are deaf, unable to talk, or perhapse suffer from other disabillites such as downs syndrome. If they use Makaton then it is your lucky day as it is by far the simplest to learn and use! You do basic signs along with saying clearly what you mean. See below different ways to sign 'are you thirsty? do you want a drink?' in Makaton, SSE (sign supported english) and BSL.
Makaton:
3) Talk to their parents. Are they deaf? Does their child prefer to communicate through signs, lip patterns, or even writing? Everyone is different.
4) Be aware of some sensitive subjects, for example cochlear implants, deaf schools, and BSL.
Some people are strongly against cochlear implants as they can be large and unattractive, not as good as hearing aids, and some people just don't like the thought of hearing all the time- if you were born deaf suddenly hearing things constantly may be frightening and disorientating. Other people believe if you have the chance to give a child better hearing you must take it.
Deaf schools mean that deaf children are taught clearly in an environment that understands their needs. However, some people believe it can isolate deaf children from the hearing world and may hinder their social development.
The use of BSL an sometimes be frowned on as it is thought that it can hinder the child's language skills and their development of others forms of communication, such as learning to talk and lip read. BSL uses a completely different structure than spoken/ written English and it can be hard for a native BSL user to switch into writing in proper English when they communicate in a language with different orders and grammar. Using BSL also can limit vocabulary as BSL doesn't use words like 'and' and uses simple words- you wouldn't sign 'convay' but instead sign 'shows'.
Like with all views, don't choose where you stand on issues like this until you have done some research, to try and avoid embarrassment or upsetting anyone.
5) Read this post: http://talktomyeyes.blogspot.com/2011/07/help-i-have-just-met-deaf-person-and.html as it applies to children too :)
6) learn some sight games, like peek a boo if they are little. Always bare in mind they cant hear you, so maybe playing hide and seeks isn't the best idea, if you cant find them then how will they hear you yell 'ready or not here I come!' or 'I give up come out' or 'omg there is a fire get out'. Just a thought.
7)If you want ideas of gifts, now a rattle is off the gift list, find a toy that vibrates or lights up. some deaf children may still be able to hear so may enjoy a musical present, but what you don't want is a child unknowingly driving their parents mad by setting off their toys... oh wait that's most children, aha. or just a classical one that isn't kinetic. Be careful googerling 'vibrating toys' though....
8) Keep them involved, in group games it may be easy for them to get left out or confused, so keep and eye out and make sure they are involved. If you are in a youth group or school perhaps arrange a deaf awareness event and teach some children basic signs so that other children can communicate without an adult having to be involved. Make sure everyone is aware that being deaf doesn't make you exempt from anything.
9) on the point, if you are arranging activities and there is something no suitable for deaf children, don't make them sit it out! adapt it or make your own game up! have a look at good group games that you don't need to hear to do here: http://www.irishdeafkids.ie/2008/group-games-for-deaf-and-hearing-children/
10) Being deaf is a disability, but try not to make the child feel different. Don't blame everything on their deafness, treat them differently when they don't need to be, or punish them any more or less then other children. At such a young age you can be taught to feel certain ways about things, so be sure to never make the child feel like they are an outsider, or exempt from the rules that apply to other people.