Its really odd..my 5 weeks old kittens doesnt pee..?

i have 3 kittens..and they were 5 weeks old..but i always wonder why they didnt pee..im talking abt the ****...as far as i experience..i only notice they urine only..its weird..the last time i saw when they were just born..i saw some shits on the junk clothes at their nesting place and my cat [ the kitties's mom] ate it..tat was the first and the last time i saw it..but now recently they didnt **** at all..i nvr saw it again....if u think that the kittens' mother ate it..i wud hardly believe..because i always be on my cat's side..every dae..every minute..i play with them..im not a busy person..so keeping my cat company is most important time to me...so wat can u say abt this issue? thanks