I dont eat out a lot with the boys in st hellier or st aubins as we live in St ouens and we tend to go to our favouirte beach cafe El Tico right on the beach amazing veiws relaxed atmospher and great food i would really recomend.
But in st Helier
I love cafe Jac which is at the art center its busy at lunch times so might be worth booking this is there menu
http://www.cafejac.co.uk/secure/resourc ... nu_web.pdfI dont know if you like Thai food but there is a great little thai place and they would make you a small portion of anything you want its called Park house.
St Aubins has some great resturants i have only ever eaten there with friends so not sure what they would do for children but Mash, the Salty dog and Dannys at the harbour view all doing great food and i think they would be acomadating for children.
Feast in Gorey is really good ive never been in with the boys but i think they will do anything off the main menu for children. (i know thats not st aubins or st hellier but its easy to get to if you dont have a car)
Your hotel will be able to give you directions to any of the places i have sugested. What hotel are you staying at?