Baby won’t walk

I’m a foster mom to an almost 18 months old and she still hasn’t started walking or furniture surfing. This may be do to drug exposure so I can’t be mad but I’m frustrated. I don’t understand how someone could do this to their baby, I know addictions are tough but how couldn’t you stop for your child? She shakes and went through awful withdrawals as a newborn. I hope the best for these moms and hope they get their babies back but I just don’t understand some of the decisions bio moms make sometimes. (I made another rant here earlier to about my foster sons situation ahhhh this is so stressful and I don’t have a outlet)