This is a good question, because there is nothing more important than a thesis in writing a paper. Keep in mind that you will need good reasons for your thesis. So, in the light of this, let me give you a few suggestions. First, one interesting thesis can be to look at gender differences between boys and girls. Are girls more mature in the early years? If so, why? You can do the same with gender development in terms of motor skills. Another route to go is to explore abnormal development and learning disabilities. Can these disabilities be corrected? Another very interesting approach can be sociological. Perhaps, you can look at the role of television and video games in the development of children. What roles do these things have in the development of children?
You have a rather broad topic for a paper. You need to narrow it down to a specific focus within Early Childhood Education. There have been books written about Early Childhood Education, entire classes devoted to it. There's A LOT to cover, and there's not way you can cover it all in one essay or paper, unless you're planning on writing a book.
A good thesis statement contains a topic, a focus and an opinion. You already have your topic--now you need to find your focus. Racial biases in early childhood educators? The different types of certification needed to become an early childhood educator? The benefits of early childhood education? The benefits of 4K versus starting a child in kindergarten? Special education considerations in early childhood education? The best way to set up a classroom for a preschool? Classroom management strategies for an early childhood classroom?
See? I teach at the high school level, and I was able to come up with many focuses for your paper.
Once you have a topic and a focus, your thesis needs an opinion--even if your paper isn't persuasive. The opinion doesn't have to be completely and totally one-sided. For instance:
The best way to set up an early childhood classroom is to provide visual stimuli combined with spaces children can call their own.
Someone could argue that, insisting the classroom should be free of visual stimuli and students should be required to sit at desks.
Children are often unaccustomed to the idea of school when entering a 4K classroom; therefore, it is the teacher's main duty to teach students how to act in a school setting.
Topic (ECE) + focus (what is taught) + opinion (how to behave a school is the most important thing taught) = THESIS