Dog/Wolf - Great work.
Frog - Awesome
Cow - Udder needs some work... and the whole thing is just.. meh.
Mushroom - Frankly, not very good.
Tree - See mushroom.
It looks like you posted in order of drawing them (older = lower) so keep it up and you'll soon be one of the greats.
If you didn't do it in that order, keep it up anyways, but try to make the plant ones... better.