My girls are about 2.5 months old and i started giving them small amounts of mashed tuna and vienna sausage... just read that they should also have some grit to help grind down the food i their gut. What kind of grit should i look for? I make sure the tuna and vienna sausage is super mushy (put in a food processor). im hoping to give them some yogurt next month. Want to be sure im not doing anything to hurt them... I love treat time as much as they do!