Walking

hey was just wondering if anyone has this problem as I keep getting told its a boy thing my boy has just turnt 3 but having problems with getting him to walk his nursery is at the bottom of the hill where we live its a 3 minute walk but this is just not here it's anywhere his legs are fine he loves to jump on his trampoline and is fine in nursery he won't walk up the stairs where we live I know it's alot as we do live on the 3rd floor with no lift he started walking up them on some days but he hasn't for a few months now he won't walk down them his fine when inside as we live in a masonett his not on the lightside ither i struggle if I use his buggy as he dose not like going in there as he thinks we getting in the car all the time I've stood my ground so many times on trying to get him to walk but he always ends up on the floor screaming I can be very firm but this can last up too 15 minutes his non verbal and has autism I just don't know what to do he will walk a few steps when outside but then wants me to carry him this is everyday now has anyone got any tips or advise to help me get him walking a bit more I know his only 3 I've already been told I need to get him walking more but how do explain to child of 3 who is non verble I've been thinking of getting him a little scooter but don't know please anyone that can help I'd be really great full