B12 is not an easy subject to get definitive answers on. I'm not keen on just taking a supplement in case it might be needed, in fact I think supplements are certain to have unbalancing effects in the body. However, sometimes lack of knowledge (by everyone, not just us) means we do something in the hope (rather than certainty) that it is right.
We decided that it was better for my 'beloved' to take a B12 supplement rather than chance things if there was a deficiency - but we did this after quite some time (when our son was 18 months and still breastfeeding frequently and thus being his primary source of B12). I looked up quite a bit of info regarding supplementing with B12 and reached the conclusion that a sublingual (dissolved in the mouth under tongue) supplement would be the best. Haven't got time to go into all the reasons now, but in a nutshell it appeared to be the most efficient way to get B12 into the body, bypasses any problems that might exist with absorption in stomach, other than injecting it seemed the best.
Here is a link to the ones that we get, not sure if they are available in the USA etc, but they are in the UK: