I'd encourage the parents to go to the pediatrician, but I heard from a friend that her pediatrician told her not to be concerned (when her child was 17 mos and not walking) until 21 months! My sons ped told us 18 though so I suppose it depends on the dr.

Not sure here you are, but in AB, parentlink has an ages and stages questionnaire and I think the 24 mos one has quite a bit on gross motor, if you get a chance to fill one out, they're pretty helpful! We had one done with my oldest when he was around that age. If you aren't in alberta here's a link to the online version, but I haven't gone through it, so hopefully you get the full version.

https://asqonline.com//family/1393-s...-english/start