Nanum,
where are you from? if you really wanna have fun with your kid check out the laconner smelt derby (should be next weekend).... i grew up doing that every year... it was a blast. they have prizes for anything possible for any age group (i won 20$ when i was like 9 for snagging a fan belt off of the bottom and entering it)
go to the baitshop/hardware store and buy gamakatsu brand jigs, the ones with the little orange weight are the best ones out there.... i find the smaller the jig hooks, the better the results. get some chicken feed/chum, toss it in there.... find a dock somewhere, and drop the line in the water.... start jigging. if you are in skagit county, try the shelter bay marina, or the northern most marina docks in laconner, the oak harbor marina (the higest producing smelt hole ive fished), or cornett bay (never had any luck there however- lots of guys swear by it)
if they are there, they are there, if they arent.... well its either because of the tides, or they just arent there.