If some routers are better than others i dont know, but i use this (3500L) router with dd-wrt to do exactly what you want. I restrict the young ones to access the internet at certain times and i have different settings during weekends. Any router that supports dd-wrt can do that and i suppose tomato and other firmwares can do it also.

If you want to block certain sites that would not be a problem, for more advanced content blocking someone else has to answer.

Great reading before you upgrade: http://www.dd-wrt.com/phpBB2/viewtopic.php?t=51486 Netgear 3500L Tomato beta 22 and 3x Fonera 2100 Gargoyle 1.3.5