When planning a lesson for children of this age group for the first time, you need to think about classroom management. Aspects of classroom management are different and also more difficult in this age range. If you're teaching just one lesson instead of their regular teacher, it's a good idea to use the same techniques this teacher uses. You won't have time for the children to get used to your way of doing things.
Speak to this teacher to find out how she indicates the end of an activity, how she signals to the children to be quiet, to work in groups, to stand up, etc. Alternatively, you could ask to observe the lesson and see for yourself first hand. If you are starting with a new class and you will be their regular teacher consider how you will deal with these aspects and always use the same signals.
Children of this age group also need a lot of variety. They have very short concentration spans and need lots of change. I would suggest changing activity every 5 to 10 minutes. You'll find that when you move from teaching adults to young children, you will do a lot more preparation at the start. However, children accept to repeat a favourite activity far more often than adults do and even ask to sing their favourite song or play their favourite game. This means that as time goes on, you will be doing less preparation.
It's a good idea to plan a lesson around a theme. You can take a song or story and develop the theme. For example, with a song or story about food, you can extend the vocabulary. You can also incorporate craft work, but remember that not all children of this age have learnt to use a pair of scissors, a stick of glue etc. Also some children are much quicker than others, so you'll have to help the slower ones or find something to occupy the faster ones while the others catch up. Writing will be kept to a minimum - just copying - or you may not include any writing at all. It's a good idea to give them something to take away to show their parents, for example a sheet with pictures of food that they have coloured in.
It can be very difficult to teach young children at first, but if you persevere I'm sure you will enjoy it.