I’d defo go and get them properly measured but also bear in mind that they don’t need shoes until they’re walking and it can be better for them to go barefoot until then so they can feel their feet on the floor. My eldest was a size 4 for his first shoe which was at roughly a year old. He’s now an 8 at age 3.5 so it does sound about right that a 6 would be average roughly for a 2 year old but everyone is different, if your baby is tall they may have bigger feet too x
I haven't got shoes yet because my boy isn't cruising, but a size 4/5 is the "average" for their first pair of shoes, however like anyone their feet can be bigger of smaller than this. My eldest was a size 6 around age 2, however, my youngest seems he is going to a size 6 a lot sooner than that. My best advice is to get baby measured at Clarks for their first pair of pre walkers and then you know you have the right size as they need growing room in them too and a lot of places do a cute little picture for you to keep🥰 x