The planets song is a lovely way to introduce the name of the planets to the children. I have used this song before The Planet Song – 8 Planets of the Solar System Song for Kids | KidsLearningTube (youtube.com).
Another way to introduce the lesson could be to read the book ‘My first book of planets’ – that could be a cross curricular link to Reading. This book could be read before the end of school each day.
The children could simply ‘make’ planets from balloons and paper mache. This is great fun and the planets can be easily identifiable from their size and colour. E.g red for Mars, blue and green for Earth. The balloons could also be blown up big(ger) and small(er) to demonstrate the size of the planets.
Before the lessons about planets I would slowly introduce the vocabulary needed for the lessons such as Solar System, orbit, planets, moon, space, stars, The Sun, The Milky Way.