Fabric Sailboat pants for Baptism outfit

I was just asked/volunteered to make pants for my youngest cousin's baptism (in 2 weeks). For many reasons, his baptism was pushed back and now it will coincide with his first birthday! Obviously he doesn't fit into the family christening gown, nor would that be practical on a 1yo who crawls and climbs everything. I just made a Sailboat skirt yesterday and loved it, so I told his mom I could make him a pair of the pants since it is so hard to find white baby boy pants for a 1yo (wearing size 12-18mo RTW). I am thinking a nice baby wale corduroy would work well? I thought of linen or something dressier but it is winter here. They will be white and he will probably never wear them again as white pants on a crawling baby are not practical. I also want them to be full length and I might omit the vents? Or will that take away the charm? I took a quick measurement today (not sure how accurate as he is a wiggleworm) and got 12" for his outseam so I am thinking I might not even need to lengthen the size 12-18months. He is a shortie but delightfully chubby. All and any suggestions and tips welcome! I won't be able to try them on him so they need to fit reasonably well! He is in diapers but disposable.