How long have they been sitting? Since they are Serama's, they are probably pretty serious about sitting. You can give them some eggs now (that are due to hatch) and they will hatch and raise them. Chickens cannot tell time - they don't know if they have been sitting 3 days or 3 weeks. If you are concerned about them, then you can hatch the chicks and give them to them at night. Be sure to check on them in the morning and make sure they are taking care of the chicks.
Also, what breed are you hatching? Keep in mind a Serama's size. If you give them large fowl chicks, they might not be able to keep them warm until the chicks feather in.