According to developmental studies (and don't ask me why age 5 is an overlap, I am not the one whom created these):
- Newborn 0-3 months
- Infant 4-12 months
- Toddler 13 months to 35 months
- Preschooler 3-5 yrs
- Kindergartener 5-6 yrs (I included this because it is good to know.)
I kind of agree with last two I guess 5 can fit in both slots. But yeah they kind of got cruddy names for developmental stages but what ya gonna do about it. I have mass pet peeve with clothing manufacturers and the T but I do understand maybe not wanting to put letter p on clothing. Newborn is also fine. However I find infant and toddler very broad age group, is your 4 month old same as your 9 month old, probably not.
For me I have added couple things to infant and toddler area because I see the difference that science hasn't quite caught up to.
- Infant 4-6 or 7 months obviously every child is different
- Pre toddler 7 or 8 months-12 months
- Young toddler 13months- 23 months
- Older toddler 24 months to 35 months.
The rest is reasonable as is.
The term baby can be numerous things depending on circumstances.
I don't know why but it bugs me when a parent calls their 3, 4 or 5 yr old a toddler they really aren't. If you want more general way to refer to children: baby 12 months and under, toddler 1-2. Little child/little kid 3-6 yrs, big child/big kid 7-9 yrs, tween/preteen 10-12. Though don't be surprised if 3-6 says I am big — they want to be bigger then they are.