Paradoxically, although most people considering a short or long career in EFL think first and foremost of teaching in mainstream schools (primary/secondary), most TEFL courses are focussed on teaching adults, but offer an optional, additional TYL (teaching young learners) module. Teaching children is not very different , and most people apply the required level of common sense when handling classfulls of them. Schools usually provide text books and resources for teaching young learners. I would imagine that very few CELTA or other TESOL graduates bother to take the extended course.
Although there is no internationally recognised accreditation for TEFL certificates, most certificates are recognised worldwide, but their worth is based on the course providers' reputations. Generally only specialised language institutes and colleges, and universities will be fully conversant with the infrastructure of TEFL certification, while mainstream schools that do not have a structured English department and only employ a few native speakers are more likely to accept certificates on face value. They also often pay lower salaries and offer less impressive working conditions.
CELTA is a household word everywhere, and other courses are not always cheaper. Probably none are better and CELTA standards are what most self-respecting course providers aspire to. But beware of scams - we have heard of some that have operated in Spain.