You really need to have a plan in place for when you tell them .... Such as how long your going to work and how long your going to take off after the baby is born ... Anything longer then two or three weeks then you risk losing your families .... Also what about dr appts ? Will you've closing? Scheduling at night ? Or having someone come in to look after the kids while you go such as your mil or other family member or friend. The better plan you have in place the more secure parents will feel .... If you just say I'm preg and I'm not sure what's going to happen they are going to start looking for new care ASAP . Good luck and congrats