If you don't want to do the leg work, then they would have to eventually on their own.
Cuteness has little to do if a baby/girl/boy is shy infront of the professional camera.Family members taking pics is one thing, pros - another.Filming commercials means full day of work first of all, call time often is at 6 am.You as a parent will have to be there often to at least deliver your babies on the set.Often parents stay on the set and the younger the child,the more the parent will get involved.Babies get nervise,cry,get afraid,get stabborn,have wrong attitude and ideas.Parents act like an interpreter and a guard dog.

Needless to mention,you will have to sign tons of release forms,which are often given at the end of the shoot.You do legal work and duties as well.
Agency.
Look for the agency that represents children.See what they require.They often have open auditions where you go to get seen.Many nowdays have websites and allow you to submit pics electronically.You do not need to submit professionally done pics to an agency.In fact,many request polaroids.
Finding the right agency and the one that's capable of finding you work is one of the key elements to success.Attending some acting class would be crucial.If there is a children theater,get the children there asap.It has been said tons of times,but people still get trapped into illussions,so i will repeat again: no real agency will charge you any money upfront.They make money ONLY if YOU make money.End of story.You DO NOT have to shoot with their photographer,and you should be looking for a great one for the portfolio.If the so called agency is insisting and trying to sell you 600 dollar deal,run away.Stay away from modelnig schools,most of them is scam.A real agency will have their coach to teach your child how to pose,walk and talk and such and can reffer you to specialists.In smaller market you might have to find teachers yourself and pay to them just like pay to photogs.In larger markets such as LA and New York,they take care of everything.And you can always go as a freelancer.Many people do better as freelancers and many agents are simply incapable of finding you work.Now,if your "agent" is sending you to an audition which is for everyone, that is a cattle call.You should be only sent by your agent to auditions that MATCH your description.Believe me, cattle calls can be found on your own and you do not need an agent for it. Go to www.modelmayhem.com - the site to mods and photos,and make-up artists.It is free to join,open a page for your girls,load pics,and start searching the photogs in your area.

Presentation.
Great pics are the must. Don't rush into buying a photographer untill your girls practice at least a few times with the photogs offering TFP,and TFCD,which stands for time for prints and time for cd.Which ones are better is hard to say,depending on who and how is shooting and what you want.
FInding TFPS and TFCDs is easy,go to craigslist.org,find section called GIGs, find talent - there you will find plenty of models and photogs,and actors,and commercial people looking for anything and offering anything.Contact them and offer your children as models for a test shoot.You will get very little from it,perhaps a couple small resulution pics,but your girls/boys will get the needed experience.
It may take a year,more or less for them to get comfy and understand what to do,learn and deliver facial expressions and coordinate that with their body language.

The next thing is the networking and establishing "the look".It is that something that sets your child apart from everybody else.Not nessesarily beauty alone,but perhaps charisma,special features,special charms.Or maybe there is something funny about your child that makes it both funny and cute and that could be a winning combo.Developing your "look" might take some time,perhaps years.It takes changes of the hair,the make-up,the outfits,the expressions and styling.

 Networking allows your children to be seen.The industry has a lot to do with who you know and who knows you.People's memories are short,so whoever comes to mind first,stays there and gets the gig.

As for a child model,a child would need updates of pics every year or so as they grow.Keep in mind and mind your pocket.;-)
And remember,a model is born in front of the camera,but the career is made behind it.As with any career, it takes dedication,passion,will power,guts,intuition,trials,and investing like in any business.Be willing to go an extra mile for your own good and remember that no one will do that for you.

If you did find this information helpfull and would like to learn more, I am available to teach your children how to model, establish their look,take their pictures as a practicing routine.I do have experience working as a modeling instructor in one of local modeling schools aka modeling SCAM.;-))