It can only be used as an adult. Make sure of a few things before you use it or it'll go to waste. Thisngs to make sure of;
1. You have 2 tamas, one boy one girl
2. they have both been adults for at least 24 hours (they can't have babies before then)
3. you only need 1 love potion! Only one tama has to take it just before they connect for it to work.
After one takes the love potion, connect them via present or visit. This connection will make them fall in love. Then, connect them one more time to get them to have babies. If all of the above criteria is met, then you should have 2 brand new babies!
KM