My kids more Aggressive

I notice that my kids right now is more aggressive. One time they both played outside after a minute my daughter cried because her kuya grab her toys but my daughter don't want to give. I make my daughter stop crying but still she didn't stop. So, I talk to her kuya and make him understand eventhough it's hard to explained to him because of his early age. I teach him how to forgive but sometimes he didn't apply to his sister. It's really hard to be a mother in a two little kids. hhehe