Often developmental delay is the term used when a child is young—less than school age. It just means that development is slower than expected. A child could catch up or they may not.
Children are not usually said to have learning disabilities until they are school age. Legally, many states define learning disabilities in terms of a discrepancy between achievement and IQ. In other words, a child is behind academically when IQ would suggest this should not be the case. Others define learning disabilities more in terms of processing difficulties—which allows kids at risk to be identified more they fail. For example, certain auditory processing skills are known to be necessary for reading and a child who has not been yet been taught to read can be tested for these.
My own child had speech delays and fine motor delays–both risk factors for later being identified as learning disabled. In other ways, though his development was typical and thus the term developmentally delayed was never used.
Beth
Beth