I didn't think it was uncommon to not have very many words until they hit 2?
My son had several bursts of words, but it was around 19 months that he started saying more than the standard dada bab etc. It took him a while to even say mama and he had to call me bab for months!
Honestly, its shocking how it is literally like a 'burst' of words! Just keep talking at every opportunity, talk them through everything you're doing etc. If you're busy doing housework and theyre playing with toys, put cbeebies on. My son is now 2 sunday just gone, for a while hes been able to count 2, 3, 4, 5, 6 which he could say before he could say mama, so i thought that was impressive. But there was a show on numbers last week, and out of nowhere, half an hour after watching the show he was able to count 1, 2, 3, 4, 5, 6, 7, 8, and sometimes including 9 and 10. All from watching a cbeebies show! haha He's only just the last few weeks stringing together words by himself a little better. so 'pick up' and a little less clearly 'want to get down now' after eating dinner.
It will be in their own time, but it'll be out of no where and you'll be shocked and wont be able to shut them up! I don't think its a problem just yet!