At 15 months, how much should the LO be talking ? My LO is only saying very simple words like "NO", "Ma Ma", "drop" (he always drop his toys from the high chair), & other babbles .. unlike my elder one who already spoke simple sentences at 18 months .. Are late talkers and walkers slow learners ??

At this age it is hard to make a comment on their learning ability. Some are slower in walking or talking but doesn't mean they are slow learners. Eventually they all catch up. Don't worry as they have their own development pace. I feel if u want them to talk more you can try talking g to them a lot,pointing out things and naming them. They will imitate us. It is just like how babies of the same year born but different months will end up in primary one tog. Doesn't mean the ones who are born in dec will be less smart, eventually they all catch up. Don't worry dear