How can i tell if my trainers are fake lacoste?

i brought my son some inf lacoste paris bebe trainers and have got a suspician they are fake can some1 help me how 2 tell,on the inner tag theve got the lacoste logo and size details etc.but they also say made in vietnam and then hecho en vietnam,there is a croc at the end of the velcro and lacoste wrote on the toungue.please helpme :( xx