C is good for your price range although I don't really know if it's where I'd take an infant and a 5-year-old; at lunch in good weather though you can sit on the patio and perhaps if the 5-year-old is antsy, walk him/her around on the seawall a bit.

The Fish House in Stanley Park is consistently good (if not spectacular or daring, like C can be) and I think they won't have a problem with the children either.

Parkside Restaurant is not open for lunch but they do open early for dinner in the summer, and they have a very pleasant patio. Well-behaved children do fine there. They have a prix-fixe menu at $49 for three courses with supplements if you want certain items (foie gras and so forth); they are not a seafood restaurant per se but there are always seafood options.

Suggest you check out the menus at these places to see what looks good. Also I recommend mentioning your small fry at the time of reservation so they can prepare a suitable table/booster chair or whatever :)

Enjoy!

The Boathouse near the corner of Denman and Davie Streets. Beautiful view of English Bay and great seafood.

stacy