Thanks.
1. עדה (`eda) - a pack, a group, an ethnic group, "the people", a large group, a certain group. Mentioned frequently in the Tora, calling the `important` people of Israel an "`eda". Those who`s opinion and awareness is important. It is related to עד "`ed" - witness, to experience things together, share them.
Today usually used to describe an ethnic group like: "ha `eda ha etiopit" - the ethiopean jews, ha `eda ha kurdit - curdish group of jews, etc. Or as a common word for a wolf pack: ``edat zeevim`. The usage of the word here is in order to make it sound more poetic, it is not used in this form any longer in formal hebrew, only in literature. But it was also selected to make it sound like a really large group, a horde of babies. The word рой is like a swarm, большая стая, орда.
תינוק Tinoq means baby, derived from `ynq` to suck, to draw = a breastfeeding baby while טף Taf is probably of imitative origin, like the funny noise little kids make when they run and tap the floor quickly. And as being soft. Taf is mentioned in the Tora as a generic word for kids. So technically תינוקות barely can run for distance on their own, and taf wouldn`t sound good in that song. A selection for poetic reasons again. To say группа детей, would be more accurate technically but less accurate translation as the origin itself holds that `mistake`.
2. За иорданом гремели пушки
а мир восстановился в конце лета
и все младенцы стали взрослыми
и опять на холме дом возвели

Но у побережья иордана...