Forgive me, but what is the tabernacle?
First, don’t worry too much about these little details. As time goes on, you will figure them out. Take your time.
As someone else mentioned, you don’t receive Holy Communion yet, since you are not Catholic, and because you have not yet gone through the process for receiving First Holy Communion in the Catholic Church. When people start to line up, simply remain in your pew, while making space for others to get by you. (Situate yourselves on one end of the pew so that people only have to get by you once, either on their way out, or on their way back in.)
The Tabernacle is signified with a candle in a red glass; you will notice people genuflecting (bending down on one knee) towards it, or at least in its’ general direction. We do this because we believe that Jesus is in the Tabernacle, hidden under the appearance of bread. Since you are not Catholic yet, it is not necessary for you to genuflect, unless you want to. If you are not comfortable doing this, don’t worry - most people won’t be paying attention to what you are doing.
As to the Mass itself, you can copy other people’s postures if you want to, but again, it is not required of you. When it comes to the sign of peace, if you choose to participate in this, you say, “Peace be with you,” and the response is, “And also with you.”
Finally, welcome! And enjoy your time at Mass!
we will be taking our two young daughters with us, 2 and 6, will they be ok there? Is there a childrens church for them or a cry room if my little one gets fussy?
There may or may not be an actual cry room, but there will be a place where parents can take their kids when they are fussy. Most Catholic churches expect children to be present at Mass along with the adults, but some parishes also have something like a Sunday School that kids up to about age 7 can go to. They return from that after the first set of readings and prayers are done, and stay with their parents for the second part of the Mass.