Hi M.,
Take a deep breath & relax. All is well. The same exact thing happened with my 2 boys. My oldest had teeth by 3 mos., fully walking at 9 mos., talking in short sentences by 1 yr & holding full comprehensible converstations with us at 18 mos. --- insane!!!! he's unbelievable & still that way now that he's in school (now 2nd grade).
My 2nd (and also the youngest) didn't cut teeth until about 6 mos., he didn't walk until 13 mos. or so, he babbled a bit by a year - but not much, and didn't even really talk in short sentences until 16 mos or so. Full sentences didn't come til after his 2nd birthday & now ... he's 5 yrs old - and he does NOT shut up!!!! lol he's perfectly fine, healthy & normal.
It's hard to go from a kid who's advancing quickly as your first child, to one who's going at a slower or more average pace as your second child. Either way, I"m sure your child is perfectly fine & just doing his/her own thing. ALL kids are different, no two are alike - even twins develop at different times/ages/etc. So breathe ... and if you're still nervous or concerned, talk to your child's pediatrician. Good luck~~!