Is having children really meant to be this hard ?

i do everything for my kids and have always tried to raise them right . I'm a single mum, my children's dad has no contact with our kids through his own choice .my two elder kids are 13 and 7 they act like they hate each other and are constantly arguing which i suppose is normal for siblings .what i want to know is ,is their behaviour anything out of the ordinary ? my daughter whos 7 literally lies about everything ive recently caught her stealing out of a shop and she still lied and said she didn't do nothing . theres never a quiet moment with her , she ignores everything i say and seems like she cant stop herself from causing trouble. she will scream and shout and slam doors stomp her feet she has a full blown tantrum over barely anything at least once a day, shes the total opposite at school and shes a little calmer when its just me and her .

my son whos just turned 13 , (he looks more like 16) his moods seem to change almost instantly ,as long as things are going his way hes lovely but ask him to do something and he goes into a mood ,will talk in a slow monotone voice and sort of slouches when he walks .he flat out refuses to wash he says he brushes his teeth but he doesn't do it properly .all he wants to do is sit in his room and play video games all day . he wont do any chores most of the time talks to me like crap . it seems like he hates me he sighs everytime i talk , i cant go anywhere as a family its either one or the other causing a scene .
i asked for help from social services and they put his behaviour down to being a teenager but hes been like this since he was little .
am i being over the top making something out of nothing ? it just feels like everyday is a struggle at the moment and i dread seeing them after school