Will my child come on better???..........?

hi my little boy is 2 just turned at xmas. he use to love other kids be madeup wen he saw them or if i took him to my mates house shes has a little lad hes 4 but this was last year and i stopped goin there so for the past year he hasnt really had contact with other kids and wen he sees them wen im out in public or somthing or if my other friend who i only see once in a blue moon calls round with her 2kids hes petrified really scared.i took him the wacky warehouse last wk an he was fine until other kids got in an freaked out went hysterical wudnt go near themim worried.i took him to a toddler group last week 4 the 1st time and he was the same there.any advice?also how do i deal wit it if another kid hits him as hes scared as it is my mates littlegirl whos 3 wacked him and he burst in to tears should i tell him to hit back or not?dont want him to be getting hit by any1 i dont no wot to do s te toddler group a good idea and will he *** out his shell because hes not really shy or ayting an my mate was like arrr hes really shy isnt he but es not its just coz hes not use to other kids and mixing with them help.