My sons will be 4 and 7 at Christmas and both love playing with Hot Wheels tracks at other people's houses. So much to buy though. I thought they could have a started set to tracks to build as a join t gift and then each have some accessories/extra to open. They have a gazillion cars so don't need more of those. Can anyone tell me which track sets are good starter sets and which extras are worth having as the many possibilities are making my head hurt x