This is a question to ask the consultant as everyone feels differently about kids at the party. There may be rules about having kids at parties depending on the product but for the most part, kids can be allowed if the hostess wants them there.
One thing to consider is if your kids can behave for an hour or two while the event is going on and ordering is taking place. If you do not think they can, it may be best to leave them at home or not attend. Maybe their grandparents would like to watch them for a few hours or they have friends they would like to visit.
If you feel that they can behave themselves for a few hours, it likely is okay, but check with the consultant. Depending on the product, kids may not be welcome due to the break-ability factor or due to costs. I find at my candle parties the kids are sometimes the most engaged as they enjoy sniffing all the scents and they make no secret as to what they do and do not like.
One exception to this is adult toy parties. Anyone under 18 or the age of majority where they live is not allowed. This is not because the consultant does not want the kids there; it is due to the law. A consultant can be fined and have her business shut down if she does not follow the rules. If she is not sure, she can also ID people. I know of reps that have left as there were minors in attendance who would not leave.