Tom was 6 weeks when put on losec 5mg a day, this is a low dose. He was approx 4 kg maybe. Ppis are not weight sensitive like h2 blockers so the range is great. There is a low, med, high and v.high for all weights but the difference between them minimal. Once both my boys were on their that dose of losec I never had to increase again. So by 9 weeks maybe T was on 20 mg the max dose for his weight which by then was maybe 6 kg. The average dose is 10mg I think. Some babies respond really well to a low dose, which is why they start low often here.
This is from the cryingoverspiltmilk.co.nz site
" Dosage and administration: Information shows that babies/children may respond to as little as 0.7mg per kilogram per day, or need as much as 3.3mg per kilogram per day. One dose does not fit all of the same weight with the same severity of reflux, and it appears to be very individual as to what dose suits each person. The important fact here is to use the best dose to suit the child. High and very high doses should be managed with the oversight of a paediatrician.
Low dose range is 0.7 – 1.5mg per kilogram per day.
High dose range is 1.5 – 3.0mg per kilogram per day.
Very high dose range is up to 3.0 – 3.3mg per kilogram per day.
The complete dosage may be taken as a single morning dose, or divided into two separate doses to be administered morning and night. It is most effective if given half an hour before a meal (1). "
So if your boys are say 3 kg (sorry not good with lbs.) then 2.5mg is still very low.