Places don't normally hire outside people for 1st shift, because everyone wants it. There's usually a waiting list of people already working there who want to move to day shift and chances are you won't be at the top of that list for a while. The only times I have seen people get hired directly onto first shift is when the place just opened, or they're driving up their staffing levels *considerably,* or it's weekends only, because weekend shifts aren't in demand. I don't know what your childcare situation is on the weekends, but there's no getting out of that-- every CNA job makes you work at least every other weekend.
I know others are saying you should be honest on your application, but IMO if you limit your availability to days, you won't even get a phone call. If you mark down more availability, at least you stand a chance of getting an interview and they might be able to work with you a little bit. For instance, could you work just one or 2 days a week on 2nd or 3rd shift? Then you could be pick up hours per diem on day shift-- in some facilities it's very easy to get extra time and you'll get phone calls like 3 mornings a week begging you to come in. In other facilities it's not so easy but at least you'll have your foot in the door.
Home health care is usually more flexible too, if that's a possibility for you.