My DD is 19 months old and is a mischievous little monkey. She was 7 weeks early so we've been told to expect thing to happen a little slower developmentally but the delays are not very obvious to me to be honest.
She understands a lot - will put things in the bin if asked (and sometimes if not!), gets pajamas, socks, water beaker, shoes etc and 'helps' to clear up toys.
When we tell her not to do things - chewing on books and then showing you the bits in her mouth for example and then yesterday she discovered that she could climb on the outside of the cot holding onto the sides and stand on the base. Not very high but very dangerous if she tumbles backwards. When we tell her not to do this it turns into a fun game of doing it and laughing.
When do they understand that we're telling her not to do something? Does she understand but is loving all the extra attention? Should we just try and ignore it not giving it any attention and not explain why not to do it or do we keep saying no until she gets it?
Obviously she needs boundaries and to know that some stuff is naughty or dangerous but I can't help thinking she's only a little monkey getting up to mischief and exploring new things.