In campkiddushis made in the dining room then the campers wash in sinks outside and come back to eat the Shabbos se’uda. Is there an issue of hefsek between the kiddush and the se’uda? When it comes to berochos sometimes this is a hefsek, so if one were to drink a little wine and go out is this a hefsek or do we say hefsek has to deal with berachos and one doesn’t need to worry about hefsek between kiddush and the meal?
The principle of kiddush bemakom se’uda, making Kiddush in the place one eats the meal, teaches us that one should start the se’uda as soon as possible after Kiddush (Orach Chaim 273:3). This means that one may not make any kind of hefsek, neither in time nor in place.
In particular, leaving the place where one is due to eat can constitute a problem. Your comparison to hilchos brochos is very apt, and the Biur Halacha discusses the issue, quoting a number of authorities who argue that even if one leaves one’s place for a short time, one must make kiddush again. However, most authorities compare kiddush bemakom se’uda to foods that do not require a new berachah after changing one’s location (such as bread), and therefore leaving one’s place will not require kiddush to be made again.
To avoid getting into a safek, the Mishnah Berurah rules that one should avoid leaving the place wherever this is possible. However, if one has to leave, for instance to use the bathroom (where the bathroom is outside), one does not need to make kiddush again.
In the specific case of the question, leaving the room to wash one’s hands is necessary for the se’uda (one needs to wash). Under such circumstances, leaving the room will certainly not constitute a hefsek, because it is needed for purposes of the meal. It is therefore permitted to leave the room for the purpose of washing (Mishna Berura 273:12, 14).