Hello and welcome "Corrollaboyzz".
Do you think you could give us a proper name please, we all try and be polite on here, your avatar name's a bit of a mouthfull, and a Yorkshire "Eyup sithy" hardly looks right.

Any way, we are all ways pleased to meet and greet new members so welcome.
The easiest material to work with and give the best finnish, with a minimum amount of preparation, is MDF. Plywood is probably stronger, but, unless you are thinking of making it into a "Dodgem" Mayfair, MDF Is more than strong enough for your average child.
Can I also suggest you read as many posts as possible befor you start to do anything other than familiarise yourself with the plans, there are a wealth of suggestions on here with many recomendations and very valid reasons to build the toy slightly differently to the plan and build manual's suggested method.
There have been very few Mayfair builders on here, so can I suggest to cut down on reading time, that you read the Toylander 1 and 2 threads, you will soon see lots of helpfull suggestions.
Regards,
Brian.