according to the growth chart, he's consider slightly underweight...beside this..
is he eating alot and how are his eating routine...and also have to see his activeness..
for his height 4 yrs old at 110 is consider a norm thou...so can see that he's growing well...just need to pump him up abit on the weight esp if he's those very active type.
hmmm.. is ur boy v small in build? cos i think 12kgs is pretty light for a 4yo.. my girl was 12 kgs when she was 1 yo... 2yo was 14kg.. cant really recall how heavy she was at 3 n 4 but i think abt 16-17kgs.. now at 6 she is abt 19-20kgs.